He's old....he's short...he doesn't have an impressive physique....and he's black. And just b/c he's one of the greatest prize fighters all-time, that doesn't mean he'll translate to our beloved playfighting.
And we all know how terrible/hamstrung WWE commentary is. That won't work well with DC. His charisma/spontaneity is why he's so GREAT calling UFC fights.
DC's boy, Cain Velasquez, is a lightskinned Mexican with comparable resume to DC...there was video of him training at a WWE facility several months ago. He'd probably get more out of WWE than my GOAT DC.