Having spent time reading the standards recently (and implementing some toy decoders) I've noticed a pattern in video codec designs, starting from the very first one:
H.261 - simple, not much more than MJPEG with P-frames.
MPEG-1 - basically '261 with B-frames, pretty simple
MPEG-2/H.262 - MPEG-1 with more complex interlacing stuff
H.263 - no more interlacing, better low-bitrate performance
MPEG-4 - absurd complexity that no one turned out to use most of anyway (3D scenes, face animation(!?), etc.)
H.264 - back to regular video, with better I prediction
H.265 - complex again?
Of course they do get more complex over time, but it seems like a cycle that alternates between incremental-yet-significant changes and huge redesigns that don't seem quite worth it.
It is an evolution, but technological evolution doesn't necessarily follow an exponential curve. It took many years for H.264 and it looks like many more for H.266. The next version may take even longer. Innovation is slowing, and it has pretty profound effects for a variety of industrial sectors.
