I started to read over the replies and followed the gender stereotyping derailing, but I think I am going to bring it back to the OP.
Why would it matter if someone wanted to have sex with you? If you’re there to sell widgets to a widget shopper, how does being sexually desirable matter?
I can tell you why I want to be desired sexually.
Growing up, I was not the popular body type of my generation. All of my female peers wanted slender, boyish-looking Backstreet Boys/N*Sync sorts of young men, and I was very much so not. I developed early, and by 14, I had a full beard. Not just a little peach fuzz or a creepy mustache, I could grow it out and braid it. I was broad shouldered, barrel chested, physically very strong, I had hair on my chest and not just a little. My jaw squared up and, while I still had a boyish look about me, I looked more like a man than my peers. I was a powerful young man, which was NOT what my female peers wanted.
So I went through my younger life romantically alone. I had a few short term girlfriends, all of which left me for someone more slender, less mannish, lighter voice, etc. When I got married, I had FINALLY met someone (at age 17) that claimed to appreciate me for who and what I was, and that was intoxicating. We made love at the drop of a hat, we were passionate, etc, etc.
And then it dwindled. She started commenting on those slender, Backstreet Boys, as to how cute they were. Darker skinned men, of which I certainly am not. Every trait that I did not possess. I felt lesser. I felt second rate. I felt lonely and unwanted.
Now, in my mid 30s, most of those guys are in their middle age as well, and they've filled out and finally reached "my level." However... I'm alone again.
I do not feel like I am a desirable human. I feel like there is a barrier between me and finding a partner because they're going to take one look and say, "I'm not ready for THAT fixer-upper." They won't get to know my personality, my humor, my intellect, my skills and intelligences, they won't get to know -me- because my meat puppet isn't the epitome of physically desirable.
I am picky too. I get it. If I look at a potential partner and I can't envision myself being wildly enthusiastic with them in bed, well... that's important to me. I have a type that I am attracted to. Slender, petite, shorter than me, though hair and eye and skin color means less to me now than it used to, I do like fair skin and dark hair and light eyes. I'm totally okay with dark hair or women of color, but if given a magic machine that would build a perfect partner for me, well, I know what I would pick.
And I want to be that pick for someone else. I want them to look at me and say, "Damn, I wanna get under that!" and then through association we get to know each other as people and as personalities. But, in the act of dating, in the act of finding a mate, one cannot ignore the "mating" aspect, if that is an aspect that is important to you.
It is important to me. I waited until marriage to have sex, and it was a mistake. We were not 100% (or even 90%) compatible. I wanted to do things that she didn't want to do. She wanted to do people - I mean things - that I was not okay with.
So now, I'm... sort of okay with a relationship starting out with a foundation of sexual attraction. We can work on the rest as time goes by. If it doesn't happen, hey, at least we BOTH got to have sex with someone we were attracted to. Good on us. If it goes past there, great! We'll see how far. If it doesn't well... In the immortal words of Lonely Island, doesn't matter, had sex.