Modern video services perform multiple encodings with different codecs, bitrates and screen dimensions, and serve up the most appropriate format that the client device can decode. Youtube has hundreds of format variants:

https://gist.github.com/MartinEesmaa/2f4b261cb90a47e9c41ba11...

Devices with AV1 hardware decoding - rare as they are - won't be obsoleted for a long time.

When you host videos with near 17 billion views you're going to want to stream those videos in as few bits as possible:

https://www.youtube.com/watch?v=XqZsoesa55w

That extra 25% becomes worth it.

Nothing will become obsolete. AV1 will stick around for a long time. And YouTube still does H.264 encodes to support old devices.

A new codec doesn't obsolete old devices. At least, not right away.

Studios still release new dvds with mpeg2 video. Online videos tend to be available in many codecs. Video conferencing tends to negotiate to best available or has settled on ancient codecs and won't change quickly.

Same comment, same wording was had when going from H.264/AVC to H.265/HEVC and again to AV1. Across the board it's 30% better Size vs Quality and with an X amount increase in compute required to encode and decode.

Each time these standards were put into ink, they were years from being practical.