Most bikes don't have kickstands because of fashion.

When "10 speed" racing bikes started being imported to the US in the early 70's, they didn't have kickstands because they were racing bikes. You didn't stop at a cafe and have a cup of coffee on your racing bike. So kickstands became associated with cheaper bikes and non-serious bikers. If you were a "real" biker, you didn't have a kickstand.

This idea never caught on in Europe, where hybrid type bikes come standard with a kickstand.

Kickstands aren't a problem on bikes that are designed for them - those bikes have a plate for mounting the kickstand and the kickstand doesn't come loose any more frequently than the seat or wheels come loose.

If you are mounting an aftermarket kickstand on a bike not designed for kickstands, however, you do have to be careful because you are going to have to mount it to frame parts. Meaning that if you crank down too tightly on the bolt, you can collapse the frame tubes. So people don't crank down tightly and the kickstand loosens. This is not an inherent problem of kickstands, but it can be a problem with kickstands on bikes not originally designed for them.