My personal theory is, that it was tumblr's original arbitrary limit of 512KB (now 1MB) that elevated GIF content's artistic quality to new levels.
Before there were all kinds of GIFs, but mainly unedited direct frame sequences out of movie files, yet there was no need to keep the files small. Yet if you wanted to see them in your dashboard stream in their full animated glory, the GIFs had to be kept under that limit at all costs.
Creative workarounds were found (minimizing frames/short loops/masking out static parts of the image) to create outstanding rebloggable content worth sharing.
If tumblr didn't have that limit, I'm pretty sure we wouldn't be seeing the current GIF-renaissance, maybe reaction-GIFs, but for sure not stuff like:
iwdrm, mr. div, head like an orange
We've been thinking this too! Cinemagraphs seem like the clearest example of this sort of file-format specific invention. The other factor of course are our phones (specifically iOS), and videos not autoplaying and taking you out of context.