First off, being worked on low priority
Second off, i personally don't like megas and would rather have them not in the game (it wouldn't kill me though since i dont do pvp). Mega have, imo, helped along a problem in the pokemon series that has been evident since 5th gen even earlier, power creep. The fact that already powerful pokemon (lucario, garchomp, gengar, alakazam, gyrados just for example) can now obtain even more powerful forms feels like a cheap way to add "depth' to the meta. Not to mention the legendary megas that are op as hell. Mega-Rayquaza has its own teir in smogon due to how broken it it. Of course theres no way we would be even able to get the legendary megas (only legendaries that we could possible get even in the non mega forms would be the latis) but you get what i mean. Theres a reason Game Freak didn't add any new megas in the 7th gen games.