It's not just that. It's anything creative, really. It can be a tech startup, it can be a book... you name it. The thing is that creators become blinded by their own perception as they lose the ability to see flaws.
The longer they work on a thing, the less they are able to understand that other people might not understand a lot of things. I experienced it myself few times with my coding projects. It's actually quite bad as you just cannot fix a problem as you do not see it. Even if someone points it out to you, it takes quite some time to admit it is a problem.
This is why having teams of people is useful. Single startup founders, game designers, writers... have inherent blind spots in their entire work.