soccer kicks to the leg were used in pride because they would set up stomps or kicks to the head. if you dont threaten with those, they can protect their legs pretty well. plus youre in a position where they can upkick you in the face, but you cant kick their head. not even getting into getting your foot caught
also from a referee point of view, there has been times in PRIDE when guys were not doing any damage with those kicks, but the other guy couldnt get up or risk being stomped. so the clock just ran down with one guy staring down at the other, it happened a lot in wand vs hendo 1 if you need an example
its just a stalemate position unless you have kicks/stomps and even then its a crapshoot