I’m a guy. I shave my armpits and my bits, while keeping the surrounding area trimmed. I don’t do it for sexual reasons at all. I shave my armpits because it’s cooler in the summer, it’s cleaner, it’s more hygienic, and deodorant actually makes it to the skin rather than getting caught up in hairs along the way. It’s also far more comfortable. I don’t know if you’ve ever rubbed a man’s armpit hair, but it ends up getting thick and gross, and it just feels rotten to have that on your body.
I shave downstairs for basically the same reason: it’s more comfortable to be smooth. There’s less friction in your clothes, there’s no hair to get caught in any seams, and it also makes it easier to inspect for abnormalities.
To suggest that there’s only one reason why any man would groom down there is a gross generalization with very little basis in reality. The only general statement that can accurately be made about manscaping is that it comes down to personal preference. We don’t all lead with our libido.