It's two fold. Amazon bandwidth is, I assume, premium tier 1. Where as ovh and scaleway are probably lower tier. Lower tier bandwidth is dirt cheap, like below $0.25 per mbps.
Edit: 3 things, it's also shared among a lot of users that don't use what they can. For everyone using 100mbps there's probably 20 who use less then 1mbps.
OVH has a pretty solid network and are very transparent about peering and utilization.[1] The network is definitely much smaller than Amazon, but never had any problems with their peering, the network seems to have ample capacity (whereas Hetzner had less reliable peering). I have several servers in the OVH network in Europe and I get consistently high speeds for Europe&US, independent of the time I test (don't have much traffic from Asia so can't really test that).
They will offer you better peering if you pay extra, but even then you're paying much less than at AWS for high traffic.
I suspect that AWS makes most profit with bandwidth while other services run with a very low margin.
Right. We have a 3EUR a month VPS serving as a backup server, it is a MySQL slave, doing a snapshot regularly and sending the snapshot off to a storage VPS. It certainly doesn't use 1mbps except when it rsyncs to the storage.
Edit: 3 things, it's also shared among a lot of users that don't use what they can. For everyone using 100mbps there's probably 20 who use less then 1mbps.