A red dot on a carbine is a no brainer -- they are easy to use, durable and reliable enough for games and face shooting, and an obvious advantage over iron sights.
By comparison, the red dot on handguns is nowhere near mature. The red dot on a handgun comes with a significant learning curve, the available red dots are not reliable/ergonomic enough for hard use pistols, and as many people do worse with them as shoot better.
I really enjoy shooting a red dot in USPSA Carry Optics, but I am still carrying an iron sighted pistol.