I don't think there is anything wrong with this because it is just how you feel. Kissing doesn't always bring out such strong emotions. Sometimes you might be more preoccupied with the kiss itself. Or sometimes a kiss is just a kiss.

On the other hand, it might be that you don't feel anything for the guys you have kissed and if that is the case then kissing them will never produce an instant emotional response.

I know for myself even if I am kissing the same person, sometimes it makes me feel very strongly while other times it has nothing to do with my emotions at all. Emotions just come out in mysterious ways. Being concerned about this is a good thing but emotional reactions are real hard to pin down so keep paying attention to them and keep kissing when you want to.