As an actor he understands his character and he gets in his head. So everyhting he says about Damon's feeling for Elena just flows easily. You can tell he FEELS it and is not just ACTING! He feels every bit of emotion he understands Damon/Elena and that really makes me ship them even more..

Bamon on the other hand, well i've never heard him say nice things about them (let me know if am wrong)As a viewer this shows that when Bamon happen he won't FEEL it he'll just ACT it