This one is easy.
1.The games havent met peoples standards for competitive play(I say this because any game can have a scene, so long as the people support it)
2.There was nobody from the 3D MK community to preach about offline tournaments, besides myself and Tom, then a few others came along.
3.Most likely, and I say this with all the activity in Cali, and word of mouth; MK9 will have a scene, and by the looks of it on the east coast, UMK3 is growing as well.
I hosted a tournament for MKvsDC, and a lot of people flaked out. The same community that was supposed to be there to help. At the end, it was a 12 man tournament, with some of the SRK community helping me out. Believe it or not, the Street Fighter community helped, and supported me more than the MK community at the time. After the tournament was over, and all the preaching I had done, a lot of them started attending tournaments.
Lets all look forward to MK9 getting a scene, because I truly believe that we are getting there.
MKE was built for that!