W's last laugh
The tax acts of 2001 and 2003 included temporary tax cuts followed by corresponding increases. Republican marketing at the time focused on tax relief, but today's press focuses on the tax increase, conveniently while the other party holds the Presidency and Congress. The GOP gets all of the credit and none of the blame, in an election year to boot. Brilliant.
Of course, at the time there was no way to know Democrats would be in power when the tax increase was scheduled to tax place. That's just happy coincidence.
The sunset provision was purely a political ploy. By keeping the tax cuts in effect for fewer than ten years, Republicans could sidestep rules that would have required paying for them, a tacit admission that tax cuts do not pay for themselves.