They commented in a deleted scene with some throwaway line about needing to travel.

I really wonder if they're going to do anything with it, but meanwhile it's pretty fair game and we're free to make up our own reasons. Though, honestly, my own canon is cracked and has nothing to do with needing a clear head for work. It's more paranoia and the nature of retcon.

(and again - MY rationalization for it. Anything anyone else does that is supported is gold with me, and I'll roll with it for fic, you know?)