There really aren't though. The reason there's only three is because memory is a commodity and margins are historically very low. It's not a very good business to be in, generally.

In the past when memory supply was short and then rebounded, many companies went out of business because making memory was no longer profitable.

And margins will continue to be low, otherwise they'll discover they don't have a moat. Commodity markets being competitive is a self fulfilling prophecy.

The companies have two choices. They either produce RAM cheaply and in large quantities, or they get replaced by someone who will produce RAM cheaply and in large quantities. Current incumbents are free to pick which of those two scenarios they prefer.

There used to be over 50 memory manufactures in the US alone. Everytime there was a bust (following a boom) there'd be bankruptcies. The lucky ones got bought out and consolidated. Empirically, attempting to capitalize on memory booms is a losing strategy.