I think it's to do with the I-know-what-I-like/and-I-like-what-I-know syndrome. And Windows users - in the majority by far, worldwide - are simply less exposed to Apple than Apple users are to them. They can quite easily spend their whole computing lives oblivious to the Mac, but it's hard for anyone else to remain oblivious to them. They're everywhere. (I don't mean this as an anti-Microsoft sneer either: I have been for 15 years and still remain a Windows user, and expect to carry on - so I'm one of Them too.)

Due to Microsoft's market-dominant position, there's a lot of good software that you simply can't get because it's written for the one customer-spending base that dwarfs all the others put together. And broadband (which speeds download time) plus good AV programmes & patch updates plus a bit of common sense mean that they are (or at least feel) protected. You can use any machine, get any application, walk into any shop, pay less (arguably: though this is changing). Windows is the biggest kid on the block, and IMHO people simply don't tend to think - or even notice - beyond that. They don't feel they have to. This insularity was certainly the case with me.

It's a sort of influence (I'm tempted to say brain-wash but that sounds too intentional and also insulting, and I mean neither) by sheer force of majority. It stopped me from seriously searching for alternatives, though I got/get furious at some of the shenanigans MS pulls. AND by the way they have you by the short & curlies if you get too dependent on any of their programmes - which is another reason users don't switch. It becomes self-perpetuating.

I am now so glad I ventured into Apple terrain, but in all honesty I would not have if it were not for the safety-net of being able to run dual platforms. My professional work is tied up in my computer as much as in my instrument, and I simply have too much to lose. Also, the music school I teach in has bought an entire stock of new computers - not just for the office staff but an iMac for every teacher as well - and completely ditched their PC system (which tells you something). This gave me unpressured hands-on learning time and I was able to get to know the Mac in a totally relaxed, risk-free way. Most people don't have such a luxury handed to them.

Your question is a very good one. I think there's as much psychology in the answer to it as there is technology, perhaps more. For many people - something like 95% of the global market - Apple is simply foreign territory, and it feels like a gamble. There's security (real or imagined) in the familiar and folks like to stick to what they know - even if "what they know" brings them some severe disadvantages. It's the status quo, and we all know how powerful THAT is.