To be honest, to this day I still wonder if the whole "Mega being the liked supermechanic" has more to do with them being the *first* one and actually present in 2 generations, rather than them being better or cooler or anything.And the entire deal of Megas not being "only a thing in this region", and instead being seen in a Gen I homage just before XY's release, playable in 4 different regions, and still going strong in GO and the like. They aren't quite the same deal as the other 3 gimmicks.
From what I recall (Feel free to disprove me on this) they weren't even planned to be in SM, they only ended up including them because of popularity. (Not a case that the first VGC format of that generation did not allow for megas despite several Alolan natives being able to mega evolve)