The difference is that baseball will often have "stints" in a city, you may play back to back days but you won't be traveling. Whereas in the NBA you might be in Houston one night, LA the next, then to Boston, and Chicago, in the space of a week or less.

Baseball is also a lot less "active" than basketball - they are certainly world class athletes, but for many positions the game is slow, punctuated by quick pushes, whereas if you're on the court in basketball you're working at 100%, 100% of the time.