I decided to ask /u/stevenrobertson (youtube engineer) why are AV1 videos using such high bitrates, here is hour exchange:

Me:

Hi, I’m a moderator of r/AV1 and community noticed a weird trend with AV1 videos on youtube. The whole point of AV1 was to deliver better quality for smaller data streams but apparently it’s not the case right now.

AV1 files have larger bitrates than VP9 and we are somewhat confused by this. Do you have any information that you could share with the community, that would help us understand how youtube is planning to use AV1?

stevenrobertson:

Hey Dominic! AV1 is expected to save YouTube and its users a ton of bandwidth over the next decade or so. Our goal today is entirely around driving adoption, making sure hardware decoders land where they need to and are reliable and well tested. We’re explicitly targeting fidelity levels that are higher than VP9 for now as part of driving that adoption, making sure decoders are fast and reliable and making sure AV1 always looks great. This is still just the start of the AV1 rollout. HTH!