I think the Steam Deck broke the invisible barrier of platform agnosticism. Sure, Sony and Nintendo had Consoles and Handhelds at the same time, but they always made sure that you get charged twice. Sony had a nice run with the cross buy for PS3/PSP/Vita years ago, but it was only for a few games technically able to do so (and at great expense for the developer as they had to create several ports of a title and only charge for one of them).
Valve did all the hard work and just gave it away. They've been giving you offers for 15+ years now, created Steam Input, created proton, created the Steam Deck, took a hit on the MSRP, released a new model so the used market got flooded with second hand offers in the span of... two, or three years? Not only they brought the easiness of use of a console to the PC space, but also created an ecosystem that can be run on any hardware. And in case you didn't already know, PC gamers don't pay for shitty proprietary memories, headsets, platform fees, online gaming.
The big three are probably seeing the writing on the wall. People won't adopt 4 ecosystems for one or two shitty exclusives. They need to come up with an angle so you want to buy their flashy hardware, their version of the same games, their subscriptions before people realize there are no perks of having 4 consoles and at least 2 of them just roll and die.
Native running Handhelds from PS and Xbox may seem not likely now, but I think they are bound to happen as a part of becoming their ecosystem more attractive to users. They pretty much are racing to fill the second place behind Steam before is too late (they won't provide more value than Steam, but they only need to outrun the other 2 really).