As others have mentioned, most of the videos are served as "gifv" videos, which are much more bandwidth conscious than actual gifs.

It's worth highlighting that Gfycat is managing to operate as a short gif/video hosting service without turning awful, though I obviously don't know what their financials look like.

Gfycat does have a homepage of popular gifs, but they've never shown them to me unless I wanted to see them. The viewer page is just the viewer.