Of course other hobbies are allowed, we don't regulate all aspects of your life.
Fitness is a huge part of the military lifestyle. Fitness contributes to better health (both physical and mental), fewer injuries, and success in your career.
Some trades you'll have a lot of personal time because your work days will be 7-4, 8-5 or whatever; some will have less time and operational tempo dictates that as well. Lots of people do things other than work out, lots of on-base shooting clubs, lots of hunters, fishers. Outdoorsmen are sometimes hard to find, because having to be in the field for weeks or months on end is enough to make the word "camping"* put a sour taste in the mouth.
Nothing wrong with having a variety of activities to spend your spare time.