Why are Republicans so much stronger/Democrats weaker at the state level?

[politicallefty]

I'd agree that you're still looking at the ramifications of the 2010 election. If I'm not mistaken, the map just prior to that election looked something like this (looking strictly at partisan control of governorships and state legislatures; not taking supermajorities into account):

Other than the Midwest, I think it's apparent that 2010 began a realignment towards a more partisan and straight-ticket voting habit. Both parties seem to have really started to lock down their bases.