How often, and why, do you change up your primary pistol generally

[Keltyke]

I never change my carry weapon unless my primary is down for repair. If I carry the same piece day in-day out, week after week, I become VERY familiar with it. Being familiar with it brings accuracy and speed. I never have to think about which gun I have strapped on and how it operates. Is there a manual safety to disengage? How many rounds does it hold? Is it second strike capable? Etc.

If your "plateau" doesn't meet your speed/accuracy needs, you may need to consider changing weapons permanently.

The "best" gun is the one YOU like, not anyone else. It will be a compromise of:

1. Fit - It should fit in your hand like you were born with it there.
2. Reliability - It should go BANG about 99.8% of the time you pull the trigger.
3. Accuracy - In YOUR hand. It's how well YOU shoot it.
4. Concealability - It should be comfortable enough to wear and easy enough to conceal so you won't leave it laying on the dresser at home.
5. Cost - You don't want to scrimp on your "life protector" weapon, but you probably don't need a $1,000 Kimber, either.
6. Enjoyment - The caliber and gun should be fun to shoot. If it isn't, you won't practice with it like you should.

[Kranq]

1983 - 1992 Colt series 70 1911 .45 ACP
1992-2014 Sig P220 .45 ACP
2014 - Glock 26 9mm

Since about 1984, my "out in the woods gun" has always been my blue, 6" colt python .357, and probably will be till I die and my kid gets it. As I get older, I'm less interested in working to dress around a heavy, full size auto.

[JustOneGun]

I never change my carry weapon unless my primary is down for repair. If I carry the same piece day in-day out, week after week, I become VERY familiar with it. Being familiar with it brings accuracy and speed. I never have to think about which gun I have strapped on and how it operates. Is there a manual safety to disengage? How many rounds does it hold? Is it second strike capable? Etc.

If your "plateau" doesn't meet your speed/accuracy needs, you may need to consider changing weapons permanently.

The "best" gun is the one YOU like, not anyone else. It will be a compromise of:

1. Fit - It should fit in your hand like you were born with it there.
2. Reliability - It should go BANG about 99.8% of the time you pull the trigger.
3. Accuracy - In YOUR hand. It's how well YOU shoot it.
4. Concealability - It should be comfortable enough to wear and easy enough to conceal so you won't leave it laying on the dresser at home.
5. Cost - You don't want to scrimp on your "life protector" weapon, but you probably don't need a $1,000 Kimber, either.
6. Enjoyment - The caliber and gun should be fun to shoot. If it isn't, you won't practice with it like you should.

While I agree that only the person with the pistol can decide what they want, it is worthwhile to discuss what they might want to consider depending on what they need from the pistol. I am assuming a self defense pistol here but the answers might change with a different requirement.
Looking at your list, many people confuse #1 Fit as how does it FEEL in my hand. I hate the way a Glock feels in my hand, but I shoot them great. The majority of humans can fit a typical handgun. Some with very small or large hands might have problems that would cause them to switch pistols. Advanced users can make gains as you suggest with a switch to a different pistol. Many newer shooters never gain the necessary skill to begin with. Often they go from pistol to pistol in search of that fix. IMHO if the plateau you have is never learning to shoot then changing the pistol won't help that much unless there was a fit problem. Then you learn to shoot and might change again for a real reason. It's no big deal if they still want to choose a pistol for that reason, but it is all about making an informed choice. We all do our best and take our chances in life.

[NH Shooter]

The "best" gun is the one YOU like, not anyone else. It will be a compromise of...

This.

I began shooting handguns regularly over 30 years ago when I joined a NRA bullseye league. I spent way too much time in poorly ventilated indoor ranges shooting a High Standard .22 and .38 Special S&W k-frames. I lived in a part of NY where even at that time, a "pistol license" was merely for owning them with the county's blessing, not for carrying concealed.

I also shot IPSC, a civilian PPC league and IDPA, which I still do on occasion. I owned a Colt 1911 at one time but could never get the hang of it, either with one hand for bullseye or two hands for everything else. What I really thrived with was S&W k-frames shooting them double action, with which I became very proficient earning Master Class in PPC.

As much as I found synergy with the k-frames, I never gave up trying to find a pistol that fit my small mitts and that I could shoot well. I picked up a S&W 5906 which I could shoot reasonably well, but still not as well as the wheel gun. Then one day for grins and giggles I rented a G17 at the local range and gave it a whirl. For the first time, I felt truly comfortable with something other than a revolver. After the range session, I went back into the gun shop and purchased a Gen3 G17C on the spot and have been very happy with it ever since. I've shot many IDPA matches with it (with an unvented barrel installed as per the rules) but living in Suffolk County, NY, concealed carry was still something I was not legally allowed to do.

In 2007, we moved to New Hampshire where I could finally carry concealed. At 5'7" I struggle to conceal a full size pistol, so in 2008 I purchased a Walther PPS in 9mm. The PPS fits my little girly hands very well and I shoot it nearly as well as the Glock, especially at 10 yards or closer. I carry it in a Comp-Tac Minotaur MTAC where it conceals well and is very comfortable.

So in response to the OP, I have only changed when I did not feel proficient with what I had, or what I had did not work well for CC. I now have a couple of pistols that are reliable, that I can shoot well and that I have gained a level of proficiency and comfort with. Until I that is no longer the case, I have no plans on changing.

But after all of these years, I still have a soft spot for a S&W k-frames, if not so much for CC.

[Up1911Fan]

Every few years I generally gravitate away from Glocks for a year or so, then go back. After spending some time shooting/training with something else I generally shoot Glocks pretty well rather quickly. 2 years ago I shot Sig's for about 6 months, never really warmed up to them but the DA work seemed to help my trigger control when I switched back. I plan on picking up a CZ P-07 and P-09 and dedicating 6 months or so to them next year.