Because unlike PCs, consoles can and do die.
If your console lose players, the console itself would cease to be. And then the games you bought for it are lost forever.
PC gamers may joke about someone having a Potato for gaming machine, but the fact is you can still play on a potato if you want. And PC isn't going anywhere because no one manufacturer is able to disconinue the whole ecosystem. PC ecosystem is a mess, but it is for all intent and purposes immortal.
Consoles are perpetually on the brink of dying. Sold at a loss (except for Nintendo), the hardware has to justify both its own existence and the ongoing development of its successor.
(Playstation was going to cease to exist if PS4 didn't launch well)
So why even have a console platform? Because it is a walled garden that offer good rent from third party game tenants. And third parties know they can make more money on consoles than on PC. But ONLY when the number of console owners are high enough.
When you don't sell enough consoles, it leads to a negative feedback loop of the console losing third party games, which leads to less consoles sold. etc.
Nintendo found its niche as a handheld company and being almost reliant on 1st party game sales. Microsoft is claiming they are moving away from the console model. Both are just facing the reality of losing their main console base of the past.
Console waring is just customers being aware of the thin ice they are standing on. That there is "not enough to go around", and that their own console would have a much higher chance of getting a next gen if their direct competitor just go away.
