Personal preference is the deciding factor in my opinion, that's all there is to it. Most people just can't be bothered with upgrading their PC to play the newest version of Call of Lol these days.
Looking at some of the people I know from secondary school, they wouldn't know the first thing about any component in a PC, they know how to turn the thing on, how to launch MSN, how to open the web browser to go on Facebook and how to get on to YouTube. Everything else is a complete mystery to them. When it breaks they go to daddy who knows nothing about PCs either and he say's "I know, I'll send it to TechGuys at PCWorld, they'll fix it".
When people finish a day at work these days they just want to come home and chill out killing some guy who lives 1000 miles away on an over-hyped console game.. or watch Eastenders. Walk into room, turn TV on, turn console on, console launches straight into the game. Said person doesn't need to worry about graphics drivers, system requirements, patches, viruses, etc. Friend invites them to a server, hours of laughter ensues, they talk about it the next day for hours.
Consoles are cheaper to buy, their games aren't, but you know they'll work.
There are so many factors, but in essence it's just down to personal preference.
I've got my PC, Xbox 360 (which has now decided to work all the time) and my PS3. I spend most of my time when I'm at home on my PC because I can do everything on it, apart from the last few days I've been on the Xbox because it's decided to work and I bought Forza 3 for it and I've wanted it for ages.
The PS3 hasn't hardly been used since we last had all the snow in which I used it to check the college website to save me getting up. The Xbox has been dead until this last week so I hadn't touched that either. I generally get quite bored on the consoles and I don't really know why, I can buy a new game and happily sit there for a day on either console but then the novelty wears off and I start to think "Well this is a pretty dull gaming experience, to do anything worth while I need to pay a subscription fee, what's the point. Screw it, I'll go on the PC".
To do anything worth while on a PC, you need a good PC. Which for most people, who aren't us, means upgrading a computer which takes more time, more money, more effort. Which people just don't want to give these days after a day at school/college/work.