AV1 is bloody awful to encode in software.
I was recording videos of lectures (a slowly moving person against a whiteboard with thin sharp lines on it, in a questionably well-lit room) and needed to encode them to smallish 720p files to be posted somewhere (ended up uploading them to the Internet Archive). This is not something that x264’s default encoding profiles do well on, but with a day or two of fiddling with the settings I had something I could run on my 2014-era iGPU-only laptop the night after the lecture and have the result up the next day.
By contrast, libaom promised me something like a week of rendering time for the three hours of video. Perhaps this could be brought down (my x264 fiddling got me veryslow-comparable results several times faster), but the defaults were so bad I couldn’t afford to experiment. (This was some four years ago. Things have probably gotten better since then, but I don’t expect miracles.)