Because Gabe is a Microsoft alumni and understands very well how they could trivially leverage their power to destroy him. If he has hardware and software he controls, then he becomes unkillable like Apple.

Microsoft shot Xbox twice in the back of the head, Playstation has the reputation of movie games hanging over it like a wet fart, and Nintendo went full bean-counter mode with the Switch 2.

Since all of Valve's rivals are busy sabotaging themselves, now would be as good a time as any to try the Steam console again.

The SteamDeck was actually successful and locked people into the Steam ecosystem pretty well

Because its realistically the only way for them to expand, by taking over the home console market.

And honestly, being able to just plug your Steam account into your big screen in the living room is something with a lot of appeal for a lot of people. The "Steam Family" thing already made huge grounds on that regard, in terms of making it an actual family based ecosystem instead of a singular person's.