You don't get it. Cruz voted for the TPA because he knows that it won't pass in this Senate as negotiated by Commander Xero. That means that if Cruz or any Republican is elected, he will then have the opportunity to negotiate a better deal and present it to the Senate. It's a term of authorization to the Presidency in principle that in effect does not apply to Obama. It's represents an opportunity to undo much of the damage done by prior agreements. That was the reason for the vote.
Since he voted against the final bill, get over it. I actually support TPA and it would have been a better bill if Cruz and Sessions amendment on immigration had been adopted.