Although I get where you're coming from. It would also be nice if all products discontinued by google would just get open sourced.
They are basically saying it's useless to them so why not let somebody else give a try.
Real-time video is plain hard, especially when latency comes into play. Having Google tackling this with their unique technology (QUIC / lots of low-level performance expertise) and resources (GCP / CDN), I'm really looking forward to try it out.
Their standard reason is that most products use tons of internal API calls/private modules and it would take a lot of hours to replace those with code they're willing to release.
Video chat has been around since forever. Having a major player like Google wade into the fray, destroy all the small fry, then bail out (as it has done many times before)? Not good for the market.
Whatever small fry exists on the market, they have survived the Skype juggernaut, FaceTime, Google Hangouts and Facebook chat. I find it highly unlikely that Google Duo is going to be a uniquely destructive force.