Matchmaking

How does it work that I get the same teammates twice in a row in ranked, literally causing me to lose 2 games in a row? One of them went 0/7 on kat to a talon, nothing to be done there, other one went 0/6 on rengar feeding various lanes, next game, 2/7 on yi, just clicking r and flashing to dive their full hp adc under tower, and their top lane yorick who just did not have a good game... why?