I just think that anytime something goes "mainstream" there is a strong motivation to keep things safe and palatable. That's why smaller, niche and startup companies can be daring. They don't have shareholders to keep happy, and they have room to be truly creative.
I do wish WotC would let their creative staff go nuts a little bit and put out some smaller more niche products that don't need to set the world on fire (in addition to their usual output, just to be clear). I don't think the design team lacks creativity or talent. I think they lack freedom.