Honestly, the TOS and TNG theme songs were different from the DS9 and Voyager themes. The former being more powerful, driving themes. The latter being more somber, contemplative themes.
It makes sense to change it up every once in a while. And honestly the more grounded, hopeful theme of Enterprise felt right for the theme of the show, setting up the eventual foundation of the United Federation of Planets at the end (spoilers, sorry).