I've been resisting commenting on this but here goes....
Huge media PC guy here. Built many of them, huge proponent of them. Did tons of different combinations of MCE boxes on XP and 7. Always had nice, quiet towers next to my TV's in all rooms from mid 2000's until last year.
But it's dead. I've decommissioned all of my HTPCs. All of my families HTPCs. All of my friends HTPCs. Without MCE, the "TV attached to my TV all the time" is just expensive and cumbersome. This is before we try to get Dolby Vision, high quality audio codecs all the rest of that garbage to work.
It's dead to me. I have an overly capable Plex PC and the right clients for my media at each TV. The only way I can justify that PC now is that its a simulation PC for my indoor biking too.
There are too many great options. Consoles - especially the new ones are fast and supremely capable. Huge QoL improvement over the last gen. Embarrassingly powerful next to any APU likely released in the foreseeable future.
Capable smart TVs. Rokus. Apple TVs. Etc. They have good remotes, remote listening, tons of apps, slick interfaces, and are (relatively) super cheap.
Want a more PC experience? Ever improving SBC's make it tough to justify anything more than $100 as solution.
Finally, building a bespoke PC to hook up to your TV? It's almost always more expensive to go SFF. Let alone the folks I know who just hook an old laptop up to their TV when they want that out of convenience. The longevity gains of the last decade really make that easy to do for some impromptu Steam Big Screen gaming. Plus you can use a laptop as, you know, a laptop.
It's a niche of a niche of niche.
That's all I can say about it, really. There will always be those that are drawn to SFF for their elegance, I get that. But I think most people want bang for their buck and nearly everything is better, especially eyed with any look to the longer term.