Why don’t I have linux and a custom rom? Because it’s not worth the time and effort for me.
I don’t have time to get my bluetooth headphones working every time I want to listen to something on my computer. It may be a simple turn on and off, it may be using the command line, searching it up and trying a million different solutions, or it may be restarting the whole computer. With Windows and other main operating systems I don’t have to worry about that, it just works. And if it doesn’t, there is usually a solution online.
For my phone, there are so many programs that required the regular operating system. And if something doesn’t work then you have to wipe your whole phone clean, then spend time to get it all back the way you want it. Updating is very similar.
No, because they have to make money somehow (either by the company that created it, the company that has the discount, or the person using the extension).