YouTube was the first to support it. They even went to war with Roku over it and Roku killed the YouTube TV app in retaliation to YouTube's mandate that all next-gen devices support AV1, so YouTube went ahead and embedded it inside the regular YouTube app.

Roku's latest devices to support AV1, so I guess either the price came down, they struck a deal, or Roku just lost to the market pressure after Netflix pushed for AV1 as well.