GeforceNow is actually a weird service - you don't only rent the GPU. Nvidia needs to have a licensing deal with the game publisher you want to play (the game you already own). They removed quite a lot of games, because big names like ActivisionBlizzard, 2K and Bethesda withdrew licensing agreements. If I only rent hardware, I don't think I need permission by the IP holder whose software I intend to run there.
It sounds exactly how netcafes operate where the public can lease a computer and play games for a few hours. I don't think it's weird they have to get special licenses just like netcafes do.
Why would companies withdraw licensing agreements? They get money from Nvidia and also from the consumer that has to buy the game separately.
They certainly aren't launching it on a different game-streaming service or intending to compete with it. Withdrawing doesn't make customers buy more of their games either - probably less.
So why would they be withdrawing from licensing agreements that are effectively free money for them?