If a Players hidden (True) elo is below his League-skill-Level he is punished by the system.
Riot implemented that system to Prevent People from trolling their hidden elo to a Low Level to Get matched with easier opponentS to stomp and re-climb the ladder easily.
Obviosly you have Trolled Down your elo Or you belong to a lower league....
Proof:
Quote from Riot FAQ:
