I'm first and foremost a singleplayer gamer, but I have played and am playing the occasional multiplayer game. Mostly this amounts to playing Halo with RL friends at LAN parties, and I used to play some MP RTS (Spring/C&C Generals ZH) as well. But even then I generally played with people I knew (to some degree, online only). But in general I still play SP mostly. I think one of the most telling things is that I have Guild Wars now, and I was all too pleased to discover that other people are only encountered in cities or in your party, not in the wild - I've only ever played with other people if the game itself forced me to. I've never traded, or even carried on a conversation of more than 3 lines. It's an MMORPG, but I play it like a single-player RPG. And I'm glad this option is available.
To me, some of the biggest attractors in a game are background world, storyline and immersion (which is why I'm a big fan of the Half-Life games, which have all these in spades), yet MP offers none of that. In fact, now that I think about it, I've only ever played much online MP with games that offer no proper background world and/or solid storyline (Spring speaks for itself (if you know it), and Generals' world/story is a joke). So I guess for me MP is a distraction to hide the glaring flaws in the background.
In that vein, yeah, the propensity of MP games these days is..... disturbing. A game cannot truly be a good game without good singleplayer (excepting games that were designed to be purely online, e.g. Counterstrike).