M$ is about online. They always have been, and always will be. Sure, the OG Xbox was powerful, but what it really brought to the table, what really put M$ on the map, was Halo and Xbox Live. From "The power of the Cloud" to Gamepass, basically everything they do is about pushing what can be done with online services. Heck, even though I expect we'll see a focus on more single-player experiences from M$ this coming gen, it's all wrapped up in the idea of providing more content for Gamepass in the end..
Nintendo is all about fun. I don't think there's really any other way to put it. They make games and systems that you can just pick up and immediately enjoy, both alone and with friends/ family. They basically make really awesome toys -- which is, imo, why they excel in providing certain gaming experiences that their competitors just can't hope to match.
Sony is basically vanilla. They do everything, and they do it damn well. It's really never a question of "why" to buy a Playstation, but rather why buy anything else. They used to rely on third parties, but during the PS3 gen they kinda reshaped their image, and now Sony's studios are second-to-none when in comes to cinematic experiences. On top of that, they have all the most popular games, plus guaranteed Japanese support. What's not to love?
