why? in jpeg xl i get an image quicker and i can see it getting better, so i know it's still loading while the avif one looks stuck for the majority of the time, which makes it look already done loading and just low quality to me.
What exactly is AVIF doing in this case that I can't do with two <img> tags at a smaller size? I can easily create a thumbnail that beats the AVIF quality in less than the 5KB delta between the static and progressive version in Squoosh.
The quick answer is: you can have up to four passes. With progressive AVIF, you let the browser avoid rendering previous passes if a subsequent one has already been downloaded. It's more efficient and saves battery.