The steam machine was good in concept, the problem was that the software was not ready at ALL and the market was too niche. Most people alrady had a PlayStation or XBox for couch gaming and most games back then that were available on steam were not that well optimized for controllers.
They basically built the foundation over the past few years with steam input and proton so they could bring it all together to make an amazing handheld device.
You gotta fail somewhere to be succesful, and valve did just that.
I think another problem with the Steam Machine was that it was still trying to be like a PC ecosystem, so there wasn’t a universal Steam Machine. It was just a PC running a specific OS, and everyone who was making Steam Machines had wildly different builds. It didn’t make it any easier for a non-tech consumer to get, and there was nothing to get excited about as a tech-minded person other than the software.
The Deck is a perfect entry level PC, and, aside from the added bonus of portability, should have been what a Steam Machine actually was.