There are several major hurdles, and no particularly strong evolutionary drive to overcome them.

The first is breathing. Fish “breath” water. Shifting to air takes a huge reconfiguration. It also compromises their ability to process water.

The second is power. “Flying” fish are actually gliders. They build up momentum in the water before launching themselves into the air. They don’t actually have the ability to flap and maintain their flight. Developing the muscles for this would likely compromise their swi.ing slightly. That would be a far bigger issue, compared to a bit of extra gliding.

A flying fish’s goal is to break contact with an underwater hunter, before reentering the water. A steerable glide is more than enough of this. There is simply no pressure to advance it further.