I dunno if the reason people are not signing up is because the avatars because I stated that I can change them if wanted. But just in case it is and people have not read that part I think I will go ahead and improve them anyway! When I have the time.
I think it's because Mortal Kombat is a specific niche. And, people love it. But there are like 70+ mortal kombat characters, and maybe opening up the pool to any real or reasonable character would draw more in. But, you're almost there, so you might not need to.
I like Goro, Quan Chi, Bo Rai Cho, Jax(who no one is picking for some reason), Havik, Rain, Baraka would need a new face, Ermac, also people love the female characters, and there are tons of them, but you can't make those, so that hurts too. Also, the boss characters are all awesome, like Motaro, Kintaro and Goro, but you are doing the Shang Tsung boss thing, so that doesn't really work.
OK I've said way too much. Good luck with the tourney. My brother is in this tourney so that's why I'm not picking one.