>It's not that I want to be that way either, I just struggle to actually care a lot of the time. 

You are not alone in this. I don't think it is intentional, or perhaps it is that the care is in a different way, or at a different time. 

>I think it helps that my wife is a bit more outgoing than I am. It helps balance things out and she encourages me to leave my comfort zone.

I reckon a good relationship is complementary, where each person brings something different to the table. If each were the same, what is the value of the relationship? I think there is value in the "diversity" of personality, thought process, and all the way down to the DNA level. It creates conflicts in some way, but that is a growth area - as long as the difference isn't in core values.