I suspect folks like these things because they are cheap, Light, small and readily available.
The drawbacks are that they are cheap, scream for aftermarket accessories and aren't useful over about 7 yards.
Lots of folks imagine defending themselves (and others) in a movie theater or shopping center.
Not possible in larger settings than face to face, arms length
Although we hear from folks who say they've fired thousands of rounds in one, I suspect they are a very small subsection of the consumer base.
There is also the problem with reliability: these things have had some problems.
A SD handgun must always work: every time.
Although I've used all them, they haven't impressed me.
They aren't sufficiently reliable, nor are they pleasant enough to shoot, for me to want one.
I use a M 38 or ( usually) a Colt Comander in 45acp for SD.
I can easily hit theatre or shopping center ranges with these handguns, and they are easily carried: and they all work, all the time and are easy to carry.
A bit pricier for sure, but reliability is the most important issue in a SD handgun, second is being able to reach beyond arms length from the holster in 1.5 seconds.