This is oligopoly. If there are less than four major players, price competition seems to stop. There's a EU study on this, which I've referenced before. More than four, and someone will drop their price to $8.99, grow their market share, and make more money. When the number of competitors is very small, and you already have major market share, it's very hard to grow market share by lowering prices. So price competition stops.

It doesn't take collusion. It's a result of size alone.