Doesn't hurt to be Harry Freakin' Potter.
Well, unfortunately there is not really a scientific reason to be blamed (although I found an article on a men's magazine site that talks about why women are attracted to vampires. And it tells men how they can compete with the vampire's allure). But I found a WikiHow article on How to Date a Musician. No, seriously.
I did look around on some forums with a thread concerning this topic, but some of the posts seemed a little bitter. They made a little sense, but still it sounded bitter. "Women love musicians because they think they can get them backstage." Some women, maybe, but not all of us. "Most women are easy and they enjoy being able to say 'I slept with the drummer in that one band'" Yeah, that doesn't sound bitter.
One kind of plausible reason is that we want a song written about us. This is not necessarily true about all women (for example, that's not the sole reason I would date a guy), but I can see the draw of that. It's like when a guy writes a poem for you; it's just a nice way to be show that he cares.
Another reason is that the ability to play an instrument is unique. Not everyone has that ability, just like not everyone can create art or compute complicated sums in their heads. It's a gift. And I can see where this is part of the allure. Creative abilities are precious and only those with creative capabilities (even if they just have a small about of ability) can really understand each other.
You also have a little bit of the bad boy element. Not every musician is a bad boy, but there is an element of danger to them, whether it be because they aren't financially stable or because they're on a fast track. And it doesn't happen with all musicians (certainly not the ones I tend to fall for) but there's often the risk of drugs or intense amounts of alcohol. Maybe some women have a savior complex.
And let's face it, confidence is sexy. And it takes a hell of a lot of confidence to get up in front of a large number of people and show your talents. I know that I still have trouble doing this and I love my writing and believe myself to be a half decent singer. So anyone who can stand on stage without wanting to pass out has my applause.
And, yeah, it's partly because I want someone to serenade me. Plus, personally I am a music lover, mostly because I am a lyric nut and I have a belief in the power of certain music. And I love a good cheesy pop ballad with a good beat every now and then. Pop Goes My Heart Anyone?
These guys are kind of awesome