Diamonds and Plats getting placed into Bronze (solo queue)

Shouldn't summoners only drop (at most) one whole division [plat 3 to gold 3] after completing their series? It makes it really un-fun for me to play during the first half of the season being a mid-gold player. I have way too many high-elo friends that got dropped down WAY too far!

Riot says: Oh, but for bought accounts, it would make it unfair to everyone [in diamond, plat, or gold] having to play in that elo. Cause if the person who bought the account is silver, they'll never win a game.

Me: What stops people from buying elo boosts or new bought accounts -throughout- the season? If they could only drop one full division [plat 3 to gold 3], yeah, it will take 2 season to drop low enough to their actual skill level. But again, what stops them from buying elo boost or another account?

Cause you can't drop someone 3 to 4 divisions and call that fair to them, or fair to anyone else having to play in those games. I basically have to wait 3 months or so and wait for all the plats to get out of silver just so I can get back to gold. What is the actual drawback? Can someone please educate me assuming you read all this ^