Might have something to do with him being terribly written and terribly acted.
I adore Scott Bakula. He was great in Quantum Leap.
So I attribute the issues with his performance to abominable writing and poor direction.
Seriously, what kind of jackass creates a lead character -- especially one who would be speaking on behalf of humanity during the series -- and present him as a bigot toward alien species in the opening scenes of the premiere?