Valve is run by one guy (so far as I know) and he's only accountable to himself. Since he's got pretty much everything he wants from the arrangement, he has no problem with spending money on what most companies would consider cost centers and turning them into something bigger.

Activision Blizzard is run as a publicly-traded company. 86% of it is held by institutional investors [0] who are never satisfied. Most are managing portfolios of assets which are, in turn, often backing retirement accounts held by individuals. There is no ceiling because of factors like inflation, "executive incentives" that the board proposes, and the ever-increasing demands of retirees. If they can get another nickel out of the business, they'll absolutely go for it.

So really, it's about the mindset of the people making the decisions.

[0] https://www.investopedia.com/activision-blizzard-top-shareho...

That article on Investopedia is from 2021, before the Microsoft acquisition. Activision-Blizzard is no longer a publicly-traded company and instead a subsidiary of Microsoft. Whatever Microsoft wants under this arrangement is what they'll get from now on.