From your lips to God's ears.
You'd probably ask why I described sex in the unsexiest possible way, for starters. But once we got that out of the way, I'd claim that oral sex is even more intimate than "traditional" biological intercourse.
To demonstrate, I'll ask you to imagine the most romantic encounter you've experienced or witnessed in your life.
Now, forget that and imagine the scene where Leonardo DiCaprio dies in Titanic so we can be on the same page. He loved her so much, he plunged into a watery grave so she could live. (I'm still waiting for the SpongeBob SquarePants episode where Jack's waterlogged corpse crashes down into Bikini Bottom.)
If you insolently defied me and kept your original image in your head, it probably had one thing in common: selflessness.
Super-intimate and romantic gestures are so because they're selfless. It means so much because one person isn't getting anything out of it except the other person's happiness. That's why the violins swell on the soundtrack and you keep making him watch The Notebook even though it's a garbage movie.
So, to circle our way around from the figurative language and back to the original point, oral sex is more intimate because it's selfless.
If you're any good at it, you know that it's work. Even if you really enjoy it, you're not the one getting the better end of the deal by any means. You do it because it's another way to say "I love you" even with your mouth full. Or at the very least, "I want you."
I'm a little too old for the Snapchat/Tinder hookup culture that seems all the rage these days. But I'd be willing to wager random people aren't often meeting up to blow each other and then leave.
You probably want to get something out of the deal other than the legend of your generosity and lack of gag reflex.
I can't speak to actual numbers, but my hunch is that oral sex is more common in committed relationships, where you're invested in the other person's happiness. And an act that's more prevalent in couples that are closer speaks to the level of intimacy required.