Nobody has ever managed to sell a web browser (Netscape's problem), im not sure why people would buy extensions when they wouldn't be willing to buy a browser.
"Forced" is a bit strong. They did the math and realized that being competitive in the browser market was not worth the $$$$ they would have to spend to get there. Given that web browsers aren't really going to make MS money, unless they manage to get full dominance (which isnt really their strategy anymore and would be difficult in modern context), it was probably a smart business decision. If the business calculus was different i am sure they could.
Google did actively slow and cripple its flagship sites on competing browsers without suffering any consequences. No amount of money will help against that kind of advantage.
I can confirm. We have a normal Google doc (nothing super fancy) that spans about 10 pages at most, and when I scroll past about 8th page in Safari, scrolling becomes almost unusually sluggish and everything starts lagging.
The problem today is that nobody can even make a browser. Even Microsoft failed, and was forced to adopt Chromium. The web has become far too complex.