What is the point of the American Express Blue credit card?

The Blue Sky cards offer airline rewards and the Blue Cash cards offer cash back, but the regular Blue card only offers MRE points.

If I had done better research at the time of application, I probably wouldnt have even bothered with getting a (regular) Blue card.

I'm happy to have a credit card with Amex, but it seems like the regular Blue doesnt make a whole lot of sense. I would assume that if you can qualify for the Blue, you can qualify for the Blue Sky or Blue Cash.