I'm not aware of a single other product on the market that offers what Valve's device does. Tons of companies offer gaming PCs and you can slap Bazzite on lots of them, but that won't get you everything the Steam Machine offers. It's, AFAIK, unique.
[0] "But I've been running a PC attached to a TV literally for decades..." yeah, you've probably been missing some HDMI features that you don't care about but others do, or had trouble with them, while any gaming console or media player will have those features and have few or no problems with them; do you have surround sound over HDMI to a proper audio receiver, with non-broken mode-switching depending on current output? Use CEC features to wake your PC from sleep? What's your color gamut like? I've done this before too, a lot, hell I did it all the way back when I needed a composite or S-Video out on my video card to make it happen, on a CRT TV before HDMI ports were really a thing. Really good support for the use case looks a lot different than what you usually get by just plugging a PC or laptop into a TV.