I don't know--I have one pet theory: His vanity was seriously chafed when he did poorly with Hispanics in 2000. Bush was popular among Hispanics in Texas and that probably hurt his feelings when they fled him in the presidential race--he has made much effort at inclusiveness.
Now, you'd think that'd tell him something about what to expect when he hands over amnesty.
As with McVain, I don't think the injured pride of any male can be underestimated in its irrational affect.