Rmoney is still navigating the Republican Primaries
Even though he has had it sewed up for ages, Romney is trapped in primary mode because he still has work to do with the base to guarantee November enthusiasm, and he wants a placid convention.
He hasn't done (another) about face on any of his RW nut issues. (Oddly unconcerned about the fact his position is still, so far, wanting to end medicaid.)
He has the ultimate free-shot Sister Soulja moment available in distancing himself from Michelle Bachman, but you know he won't take it. Can't afford to!
The overt racism probably isn't something that plays well to actual persuadable voters. (That small but key 5% of the population.)
The tax return thing is 100% playing to the basewhy would any persuadable voter accept, "if I release any tax returns those Democrats will see them..."
He probably expects a re-run of 2004 where RW nut-base turnout is decisive, and will abandon the usual move of trying to seduce the middle in exchange for solidifying the wackos.
A conservative strategy in more ways than one.