It’s violating ToS, that simple it is. Check this thread:
I just want to add that posting it here won’t solve anything, you better properly report the player who built this. (as you already did, as I now read it). But yes, everytime someone like this appears and when dev-wiped, will be complaining cause he does not know this is not allowed on officials.
My personal opinion: When it’s not blocking some passage or causing serious lags, I would leave that be.