Most of teams are actively hiring most of the time. Senior engineers spend quite a lot of time interviewing candidates as a result. So pretty much every team jumps at an opportunity to get a few developers internally as no interview process or HR involvement is required.
Also, Amazon has a really good (even compared to other tech companies) global mobility program and they'll help you to relocate even between countries if you want to join a team abroad. Our business developer, for example, relocated from Australia to Seattle.
Of course, Amazon pays for flights and hotel expenses. But yeah, economic class only :(