From a design standpoint monks have often had something of a catch-all "what the heck do we give these guys just throw some moves at them and call it good" effect. They show up in D&D and pretty early on you can see the developers weren't really sure what they were doing besides making someone who can hurt people through punching, so they just give them a bunch of "thematic" abilities and call it good. I've generally noticed that the monk classes have all kind of fallen in line with the initial D&D conceit, ability-wise, and while in some cases the balance has been OK it seems like a number of games that include the option at all have derived it from the D&D base and never really thought to do much with it, they just decided that it was a thing they needed to have.