The "why" is simple enough: your plot is probably already owned by someone else (especially since from my understanding we're talking about an S). Or rather, the game doesn't let you transfer house because that would be a very likely occurrence. Secondly, it's also to avoid exploit from when house prices were different by world. I could have transferred to a world with cheaper housing prices, buy a house, and then return to my previous server with the house.

You are not being punished for wanting to play with friends. "Punishment" is something that is done to discourage an unfair action, and that is not what the house reset was made for. It was made to prevent unfair actions, rather. So, no one is punishing you.

The real question is why buy a house on a server you're "not fond of"?