Why Beat ’em Ups don’t allow players to face toward or away from the screen

Most Beat ’em Ups don’t allow players to face away or towards the screen: example, in Streets of Rage, when you press up, the character moves up but still facing either left or right and same goes when you press down. Even in modern Beat ’em Ups, this is the case. What is the reason for this? I used to think this is because the graphics are 2D so its harder or more work to get characters to face towards or away from the screen. But even in Beat ’em Ups that uses 3D graphics, this is still the case, like Double Dragon Neon.

One more thing, if you know any Beat ’em Ups that does do this, can you post the name of the game here. I am interested on how that behaves.