It's being run through the equivalent of a virtual machine. So it's really quite similar to the layers used to abstract away platform specifics like Wine / Proton does for Windows compatibility. Instead of DXVK you have WebGL.
Why should Valve update their old games to work on Apple Silicon? They're old and only 2% of Steam users (clients?) are on macOS.
Also, this port works offline in your browser. If you've loaded it up before the assets are cached and you can play with no internet. Yes, even if you've closed the tab and open it again later without internet.
But native to what?
Windows is no longer the commonality between all users.
The browser has that role, now.
> We want people to remain online under any circumstance
Webapps often have offline-first functionality,
which is one of the biggest strengths of a progressive web app.