Well look at gta online, moders and hackers have so much more power when the session isn’t run by the company. it alao allows them to find exploits much easier if the server tools are available to run locally. Also If you don’t want people being able to give themselves all the weapons and money and mess up your game that means game states can’t transfer between servers which means you could invest weeks in a campaign only to have the server close.

I prefer locally hosted stuff but there are obvious benefits which draw game companies to choosing to control the hosting process