because device makers will not care for the DRM, but will care for the hardware decoder they need to decide to put into their devices to decode netflix videos. By ensuring this video codec is open, it benefits everybody else now, as this same device will now be able to hardware decode _more_ videos from different video providers, as well as make more video providers choose AV1.
Basically, a network effect for an open codec.
You’ve convinced me… (no snark intended)