As a 100% Linux user with good memories of that era (flying chair, Linux==cancer, etc.) I may be the best person here to actually defend Ballmer, having for sure no hidden interests in doing that. Everything changed in those years: Google was cool, Linux desktop almost non existent, cryptocurrency not even in the head of its creator, AI was a myth and the best voice recognition could offer was the hilarious "double the killer" demonstration [1]. How can we compare CEOs actions separated by two decades? Ballmer did what was perceived as useful for its company back then just as Nadella is doing that now. Perspectives have changed, hence companies and their CEOS had to adapt. I'm 100% sure that if Ballmer were MS CEO today, he would include advertisements as well, as today putting advertisements in every free corner of the known Universe is perceived as acceptable, if not necessary, which was not the case 20 years back.

[1] context: https://www.youtube.com/watch?v=kX8oYoYy2Gc

I always had the feeling MS was squeezing competitors and software vendors, not users directly.

The user hostility have made me move me to Linux systems.

Let alone ads in the start menu!

To be fair, Windows 98 came with almost-ads in the stock Active Desktop wallpaper - and promos for AOL/CompuServ/Prodigy.

AOL was stuff that people actually used however. It wasn't "random stuff".

For many people in the 90ies it was like the brand "AOL" was a synonym of "internet".

Or screw up search on the start menu

Exactly