Question

I thought it can be Fighting Type for Mega Punch and Mega Kick move. but, why?

Answer 1

This has been a thing that has bugged a lot of Pokemon fans for ages.

There isn't really anything I can say except for that it was Game Freak's choice. It might possibly become Fighting later, like other moves have changed it's typing, but as of now your in the same boat as everyone else.

Hope I helped.

Answer 2

No reason really. Game Freak logic :D
Alot of the typings are wierd, and you never know they might change the move type at sometime like they did with gust after gen I

Answer 3

Game Freak probably just wanted some new normal moves. That's really the only reason I can think of.