They used to do it just because of the licensing fees they got for games sold on there platform, it's now that times ten. Also what you suggesting is the competition is just going to stand still? The way I see it you have to do everything you can to grow your eco system(your brand)
In my opinion the whole reason PS4 is the market leader right now by the massive margin they are is because Microsoft kind of had there PS3 moment with the Xbox one and that's unlikely to happen again.
The profit they make because of every PS4 is more minuscule compared to plus and software.
There will be carry forward into this gen. The sales dominance of their other consoles is no accident. The only hope MS has to build market share is to expand the market. I don't expect MS to be competitive with Sony in the amount of consoles sold. Where they can compete is by having multiple platforms and their sum total reach matching or exceeding Sony's. That's not going to be dramatically effected by whether Sony decides to take a big loss on hardware or not.