This sort of kicks have maximal power, because it use elastic tensile of muscules. This gives maximal acceleration in the initial phase of impact(like in sprint). Why this principle almost don't use in martial arts and MMA?
As someone who's done TKD since four - and competed quite a bit - I can tell you that jumping kicks are more difficult to land (due to the time to execute) and leaves you very vulnerable. These are two critical demerits. You have to use them sparingly and know precisely when to use them. Edit: They look awesome in demonstrations though
