Summary: The Doctor and his companions have something in common.
The Doctor never stays in any one place for very long; the wanderlust is too strong for that. It’s in his blood, and that’s always been the case, since long before his first regeneration.
It’s what compelled him to steal an obsolete TARDIS and take off for the unknown, travelling throughout space and time, exploring and discovering.
In many ways, the companions he chooses are the same; they share his spirit of adventure. Perhaps that’s how he finds them, or they him, like calling to like. The wanderlust courses through their veins too, a blood fever only travel can satisfy.