Comment by rodgerd

I would say that it's two simple factors:

1. High bandwidth charges are an effective form of lock-in. Once your data is there, it's prohibitive to move it out again.

2. Bandwidth use is very poorly understood in many businesses, compared with simpler metrics like storage, memory, and CPU. AWS can run razor-thin margins on things that people easily compare to on-prem or VPS-style offerings, and then make the money back in areas like network traffic, fine-grained monitoring, and other items that as less obvious.