There are always format fanboys but it really wasn't anything like that because the MPEG4-ASP experience still had problems for the average user (it wasn't a big win on file size/quality, compatibility was not a given, people still had to pay for licensed players, etc.).
In contrast, I think H.264 hit the threshold where it's good enough for the average person and you basically never hit the case where a file doesn't work for the person you shared it with because even though it's license-restricted, most operating systems and browsers include support. Moving away from that is going to be hard because most people will not see much advantage — AV1 is clearly better on file-size but most people aren't hitting limits on a regular basis and the feedback loops are often missing (e.g. you hit play in Netflix on your phone — how many people would have any way to tell how much of their data plan that used?).
Instead of focusing on the client, what about the server? How happy would Netflix be to reduce their outbound traffic by 20%? I'm guessing it's quite happy.
https://medium.com/netflix-techblog/toward-a-practical-perce...
15 years ago there were people who said exactly the same thing about MPEG4-ASP (eg. divx/xvid). It all comes down to Moore's law and hardware acceleration.
Another thing about hardware acceleration is that on many platforms you really did not want to push 622Mbit/s worth of raw chroma-subsampled YUV FullHD video across whatever interconnect to your GPU, so moving things like motion compensation into GPU hardware was only way to actually play FullHD content. And this is also part of the reasons why is H.264 somehow special today.