There is a sort of "the current president inherits the previous person's work" going on.
Balmer was responsible for the One Microsoft reorganization which Nadella finished executing.
https://www.theverge.com/2013/7/11/4514160/steve-ballmers-re...
https://www.theverge.com/2013/7/11/4486730/microsoft-reorgan...
I dont think Ballmer get's enough credit for reflecting on his tenure, looking at what didnt work, and blowing it up for the future on his way out the door.
While late-Gates Microsoft was the king of whole technology industry, by late Ballmer it was one of many players. While they haven't decayed into "enterprise" obscurity like IBM, they weren't driving the industry then.
They missed several "trends" like mobile phones, and only thanks to Nadella they've caught up in cloud with Azure.