I think it is multi-factorial.
There are folks who carry 1911s and revos. They will never use an RDS.
There are folks who can't afford anything but a hi-power or a taurus. I've spoken to those and felt like an idiot after not being able to control my initial reaction. Some people have no money to buy anything but a cheapest gun and a little ammo.
Some don't know that RDS exist.
Some people try and find it not worth it, like you did.
Some, like me, don't think that there is a carry worthy RDS that can support a performance that exceeds that of irons. This doesn't mean that there are no people whose performance will not be enhanced by existing options, such as already mentioned vision-impaired shooters or shooters to whom concept of speed doesn't apply.
Maybe there are more reasons that I can't think of right now.