These stores and games now include some pretty invasive DRM and anti-cheat software. That's probably what's causing the CPU usage.
So for example Valorant's anti-cheat leverages a hypervisor which is always-on, and then an additional client which runs when you launch the game.
The situation is similar with the ESEA counter-strike client.
I just refuse to play games with measures like that. Especially given the fact ESEA got caught deploying a bitcoin miner with their client.
These games always have cheaters anyway, so what am I giving up all that privacy and security for?
0: https://www.eurogamer.net/articles/2020-08-30-prominent-chea...
1: https://www.techdirt.com/articles/20160705/09363534897/check...
This is entirely unrelated to Epic Games Store wasting 5% of my CPU when it's running. I can just load my own driver before I launch the Epic Games Store.