Steam also stores your credentials world readable on the file system, I reported it I think in 2016 and they just said it was a limitation. I know Epic Games takes security more seriously than Valve at least.
The primary way of attack was to trick a steam user into either uploading the token file directly, or trick the user into running an executable that uploaded it silently. If you're already tricking the user into running an executable you design, there's not much left that can be done to stop this since such an executable could reach inside the running steam process and read whatever data it likes.
I should also mention the trend towards these Vault services to store secrets is even worse, as that they effectively make all secrets on a machine world readable since an off box service can’t determine what user is making the request. And the trust on first use idea is lacking in most implementations and vendors like HashCorp in fact don’t want to add it anymore since apparently their users had problems using it and would lock their apps out by accident. So... yeah.