Is Ted perfect? None are. But his arguments are principled and intelligent. Compare to Jeb, or Christie or Trump.
Why those three? As voters we get to compare Ted to the whole list of candidates. Jeb is reasonable to compare to, he's still in first place. Trump and Christie are behind Ted, so they are not a real factor in the race yet. Christie has not even announced, and may not.
Potential Cruz supporters are probably comparing him with the SIX people ahead of him in the polls: Bush, Walker, Rubio, Carson, Huckabee and Paul. Not the 8 behind him: Christie, Perry, Trump, Fiorina, Santorum, Kasich, Graham & Jindal.
Of those in front of him Paul has consistently and clearly spoken against TPA/TPP. So have Carson and Huckabee. Jeb is presumably for it, even if he says he's not, the Bush Brand and trade deals are synonymous. Rubio voted for TPA, like Cruz, but unlike Cruz appears to still be pro TPP.
Rubio's plan seems to be to wrest the GOP establishment baton away from Jeb, and run from that side, not from the right. To keep his establishment cred he has to support Free Trade. So, I don't find that puzzling at all.