Why haven't/don't states do smaller interstate Electoral College compacts?

[Mr. Morden]

I suggested something like this here when I first heard about the NPV initiative.  I think this could actually end up getting us to a national NPV compact pretty quickly.

I mean, imagine that you combined, say, CA, TX, and GA or some similar combination such that it's a swing state with ~100 electoral votes.  It would loom so large on the electoral map that it would end up getting a hugely disproportionate share of attention from the candidates, and nudge other states towards either similarly large super-state compacts or simply passing a nationwide NPV compact to end the madness.

Or, alternatively, suppose that you had a swing superstate of ~100 electoral votes that was committed to always voting for the national popular vote winner.  This would be such a large block of electoral votes, that it would then become practically impossible for anyone to win the electoral college without winning the national popular vote.  It would be like you've de facto enacted NPV, even though only a few states have signed on.