What a puzzling thing to say. Where do you get these ideas. Trackballs have been in use for gamers since the very first video games. As far as their popularity, there is not a shortage of gamers who find a trackball superior in many ways to a mouse.
Their ergonomic superiorty is not scientifically established, but there are certainly differences. However I've been using one by preference for twenty years, and it didn't have anything to do with my wrists. For one thing, they can be used pretty much anywhere, without a need for a dedicated space. A cluttered desk is no issue. This makes them especially suitable for the kind of situations laptops can be placed in (even a bed

), although I was using them long before I was using laptops.. For another, I've found that they are much more precise when one is accustomed to them, and with the right understanding and use of hysteresis settings in the pointer software they can also respond much more quickly.
The biggest impediment to their general acceptance has been that most people learn to use a mouse first, and thus find a trackball initially awkward by comparison. They tend not to pursue usage until they become adept.
Both of my boys were using trackballs as soon as they were old enough to sit at a computer. When they went to school and encountered mice they felt that they were quite clumsy and inadequate, even after they had been using them for years.