Every other major application and service on Mac has ARM-native builds now, there’s not really an excuse for Valve. It’s especially silly when much of Steam is running through a Chromium engine, not machine code or anything else that might be difficult to port.
There’s a difference between Valve deciding to not make Mac games anymore and Valve leaving the Mac Steam client a slow and laggy mess on newer Macs. The former only affects people who want to play Valve games, the latter affects a lot more people.
I had some fun going in 2018 with friends, but it definitely felt like a theme park with lines everywhere for demos. Maybe there’s room for something to take its place focused on those demos or community events, rather than announcements that most visitors couldn’t attend anyway.