It doesnt just happen with content, it also happens with the actual features and ideas and thats a lot and a lot worse imo. A lot of companies copy other games way too much. Playing similar games for inspiriation is fine but its a different world when every feature and thing has to be inspired by the other game, "they start their game like that too and since their game is good that means such a start is good!!!11" - "they got such a door too so we need that too!". Cant you figure it out on your own what kind of door you need?
Why cant developers design stuff on their own, and then play the other game later on to see how it can improve their own game, complement their own ideas and design rather than having it shape their entire concept and idea.
Content in the end is still just a tool. Its not about what it is, its about what you do with it. I dont care seeing the same crate or wall texture in 20 different games, as long as they do something cool with it. Legal issues aside.