I guess its because once you get to a certain skill level you dont really expect for your jump in combo to land on someone, because jump ins are one of the easier hits to parry or block like fireballs. Thats why you dont really see alot of jump ins anyway in high level play. Now if you go to a beginners match youll see alot of repitive fireballs, sweeps and, crazy jumping around and random supers.
So once you learn to get around all that people just do jump in hits for pressure and if the opponent blocks they use that block stun to walk up grab and stuff or they just jump in and throw.
But i guess it all comes down to how fast you can react to the game, just like when you do random c. mk to a blocking opponent but then one out of 5 or so hits, if your fast enough it wont just surprise you and you will be able to combo it into a super or something.
Oh ya and hello everyone this is my first time posting here.