Think about it. A man's entire sexual/reproductive system is geared toward ejaculation. Just look at how many men on here (myself included) are obsessed with their own cum, before, during, and after orgasm. To us, an ejaculation, of any sort, signifies what we instinctively identify with as an incredibly pleasurable experience. To see a woman do this just flips a switch in a lot of us that says 'holy shit, women can experience what we can!"
Then there's the whole level of intensity that many women who squirt often seem to reach. Sometimes (not always, a lot of shit I see online is pretty lame/fake squirting), when a woman squirts, it's like she's not just having an orgasm, she's graphically and intensely losing control of her whole fucking body (just like us when we know we can't stop ejaculation).
Also, don't forget about the whole BDSM angle either. As a submissive male, the idea of a dominant woman squirting on me is just about one of the most erotic things I can conceive of. And when combined with the above points...forgettaboutit...
