>>58737819Because I get to enjoy an entirely new variant of a Pokemon I like (or get to appreciate a pokemon I wasn't that into before with a new spin) that can exist alongside the original. Megas do nothing for the mon, it's just a temporary power up and most of the time a pointless one at that since the same few Megas will always be the de facto strongest regardless.
A mega is like junk food. You get a little high from seeing it one time and then move on.