TSR's Super Smash Bros Thread|SWITCH HYPE TRAIN NOW BOARDING

[Gors]

The thing is that the whole gameplay element of a fighting game is its characters. A plausible DLC content for a main Mario game would be bonus stages, because the stages themselves are the "main dish" of the game - they're what effectively extends game life.

Fighting games' "main dish", however, aren't the stages - it's the characters that matter. They aren't a simple addition, they have to be balanced and worked on constantly, thus it would make sense to charge more for them.