i think the reason would be that with browsers they don't control the ecosystem enough to get away with it. I actually agree with the ban if your framing is correct (not having looked into it any further), but if they did this in chrome, people would just use another browser to access these sites. you can sideload apps as well of course, but it's much more of a hassle than doing it on PC, where people are used to software distribution not being as centralized