Well let's see first you have to get the rights for the character to be used
then the character model has to be made, coloured, textured, then there's 7 more colours maybe even alt costumes, takes extra time
Then the Character has to be animated, that's the walk, the run, the jump, every. single. attack.
Then you have to get the sound effects, visual effects, fix the frame data so everything hits as it should, make sure things aren't too over or under powered
and after tat you have to test these attacks on the rest of the roster to see what works, does this move reflect? What needs more priority?
this isn't even everything and you'd think it would only take around... What 3 Months?
Everything has to be quality it's not going to be perfect first try, and even then it still might not be the best it can be,be thankful we have patches for that, this takes a lot of time and effort.