Xbox is designed for kids, who's parents don't want them to have full access to a desktop computer and don't know how powerful of a gaming computer they need (people like to claim its cheaper but it really isn't, and it's easier to spend more on fast hardware you don't really need).
Because of this eco-system for kids, xbox has great multiplayer support (including locally for friends), and the software was a clearer focus with less bloat. I don't see xbox market going away any time soon unless people stop having kids
I guess kids suggests someone quite young, but my impression was they (xbox and playstation) were built for people in high school and younger, which is why the product makes sense. As OP pointed out, if you were 35 just getting into gaming you'd just buy a desktop.
Consoles like Xbox serve parents who aren't tech-savvy enough to hunt for PC deals and don't want their kid to have free access to the internet.
For what its worth I used to work on a parental controls app startup and this is a consensus I found talking to customers (parents), they like their devices to do one narrow thing so they can control how their child spends their free time. There are of course adults who play it but this is the core of the market, and the strongest value-add in my opinion.
Because of this eco-system for kids, xbox has great multiplayer support (including locally for friends), and the software was a clearer focus with less bloat. I don't see xbox market going away any time soon unless people stop having kids