As someone who has put too many hours into EVE online to count. I do mundane things in video games because of two different reasons.

1) The reward for doing the mundane thing is usually very direct and actually pretty decent if you commit to it. For example with enough grinding in EVE you can afford some very fancy spaceships. Or with hours of code raiding in Rust you can steal all of someones stuff by just typing in 4 digit codes for hours.

2) Doing the mundane thing in the game is still a form of escapism from doing the mundane thing in the real world. Except usually the video game isn't hardcore mode. If I don't do it and a die I just respawn. Meatspace doesn't have this luxury. In this case the video game is an escape from existential dread.