While there are benefits with game clients especially for online multiplayer games and games needing constant updates, there are drawbacks as well:
1. For single-player games that don't benefit much or at all from a gaming client, it is just an extra hurdle to run the game. It is similar if my car always demanded that I must log into my Facebook account with my phone whenever I want to drive my car, and I would be like why the heck does it require that.
"But that doesn't matter because the gaming client can run and log in automatically whenever you boot Windows!", which brings us to the next point:
2. It seems every publisher nowadays wants to have their own gaming service client, even for games that they sell on competing services (e.g. many games sold on Steam or EGS also want to install and run a third-party client like Rockstar or EA Origin or UPlay). It simply becomes messy for the end-user when they start accumulating gaming clients over gaming clients on their OS. How many installed gaming clients is too much? A dozen? A hundred? No upper limit?
3. The gaming client is yet another thing that can break game compatibility. For instance, if you have an older game that requires a gaming client to work, you might end up in a situation that you can't play the game at all anymore, on any system:
- the game does not run well or at all on the newest Windows version, so you'd like to run it on your older PC which has an older Windows version running.
- but at the same time, the client has stopped supporting that old Windows version and refuses to run on it, hence you can't play the game there either.
That is what happened to me already years ago with Steam, when Valve just suddenly decided that sorry, Windows 2000 is not supported anymore, and the Steam client suddenly just refused to run on it (it would just present a message that Windows 2000 is not supported anymore by Steam). The games I had for Steam would have otherwise still run fine on it, if only the client had not decided that "I'm sorry Dave, I'm afraid I can't do that".
4. Gaming clients, like any additional online software, can introduce more security risks and attack vectors to your PC. Both Steam and Galaxy have had quite serious security holes at least in the past.
https://www.forbes.com/sites/daveywinder/2019/08/09/critical-steam-security-warning-issued-for-72-million-windows-10-gamers/?sh=43486d8e35e1 https://portswigger.net/daily-swig/pressure-grows-on-valve-to-unplug-steam-gaming-platform-vulnerabilities https://cyware.com/news/gog-galaxy-riddled-with-multilple-security-vulnerabilities-859d95fd https://www.cvedetails.com/vulnerability-list/vendor_id-19693/product_id-52428/GOG-Galaxy.html So, while I feel quite secure to install e.g. a single-player GOG game from an offline installer to my work PC, I wouldn't really want to install lots of gaming clients on it, for the aforementioned reason.
There are other things as well, but those just off the top of my head.