What is the point of changing egg groups for mega Pokemon?

Question

For example, Mega Gardevoir loses the Human-like group (for some reason even though it is still humanoid). What is the point, and does it impact anything at all?

Answer 1

In the 3DS era, all Gardevoir--mega and otherwise--were solely in Amorphous. It wasn't until Sw/Sh that it had the Humanshape group added, and no game since then has had mega evolutions. It's a pretty safe bet to show up in PLZA, but we don't know if that game will have eggs as a mechanic whatsoever (PLA didn't), and if it doesn't then the updated egg group will be rather meaningless for it.