Because NRS is a developer who has absolutely no idea about Beat Em Ups and 3D was too much for these guys. So they went back to the roots but anyway MK had some broken stuff..
The low pokes, chip dmg, chip to death, buggy hitboxes, block button, broken cross-jump system, easy x-rays without ANY animation, lol, negative edge, which makes some combos much harder than they should be ( Skarlet combos with df moves..) ..and and and... ;)