>>35422231You know why? Because Z-moves are easy.
It's a catch-all power up for everything, that Game Freak only has to program the main attack animation for. Sure you get a few special signature Z-moves but this is the bandage they can smack on the game as a whole and some stuff might get a buff out of it, but they don't have to actually think about it, oh no sir that's asking too much.
Meanwhile making a Mega requires you to think for at least 2 seconds and requires programming for a specific individual Pokemon. You have to think of how a Pokemon could improve, how to redesign it entirely, change its Ability etc.
That's not to say Megas are perfect. With very few exceptions, the other anons hit it on the head; it should have been reserved for evolved Pokemon that were struggling competitively (Mega Mawile, Absol, and Audino could have been normal, but weaker evolutions. Take Huge Power off of Mega Mawile and keep Sheer Force and it'd be just fine.). I can at least forgive Blaziken in hindsight because it wouldn't be fair to leave it out of the Gen 3 trio, and the same goes for Venusaur, because Blastoise needed a bit of help and christ on a cracker did Charizard need help.
Metagross is another tossup; it had dived into UU in Gen 6 (inb4 GF doesn't follow Smogon, it doesn't matter retards it was still underperforming in the VGC), but I understand the sentiment. Tyranitar and Garchomp though? Didn't really need it. I can give the Legendaries a slide only because they're banned in normal non-retarded VGC years and all in Ubers anyways, but it still bothered me a small bit.
I started rambling and I'll stop, but basically Z-moves are the shotgun approach to "fixing" the game while being marketable, while Megas are the precision based approach.