Because that's the comparison we made between Jack and the Doctor.
Hmmmm. Good point.

And I'm actually wondering if this isn't part of what River's doing in prison--hiding, rejecting responsibilities, trying to step out of her life.
*nods* Yes, I can see that. And again this reflects back on a Timelord-free universe, where there is no one to 'keep the Doctor in check' as it were. Not that the Timelords weren't pretty draconian, but they represented order.