Why don't I consistently exercise daily? Why?

I just got back from the St. George Recreation Center, and I feel wonderful! Those post-exercise natural endorphines have really kicked in. This is my second week going there after a very long hiatus (many months) and I'm already feeling the positive effects.

Today's work-out was enjoyable since I took my music along with me, and the music really helped me increase my energy on the stair machine. I was amazed at the affect the music had on my body.

Because when I do exercise I nearly always enjoy it (I can't think of a time when I didn't enjoy it once I got going), why can't I be consistent about it? It would seem like a no-brainer.

Perhaps I'll never know the answer. In the meantime, I think I'll go back tomorrow morning and do some more.