I think lack of more community features is the number 1 thing. Give communities more features, more abilities to set up their home however they want it to work and look. Then communities will have the ability to also play with rewards and tweak how rewards are distributed so as to work well for the particular community. This needn't necessarily depend on SMTs, a lot of it can be done now, I think.
Talk to communities and they will tell you what features they need to grow their community and attract new people. Try it and see! They will tell you what they need.