Steam moved all its content to HTTP away from the traditional steam delivery protocols. As part of this move they moved all their delivery to CDN's.
Steam caches were hard to maintain for steam, as the ISP (Orcon, VF, Snap) owned the hardware and maintained the Windows operation system. Steam just maintained the Steam software. It was a very weird setup for such a big company.
There is some content still served from the old steam servers, but any new games are from the new CDN's.