A lot of philosophers in history are loners. And most of whom are not sexually active, as far as we know.
If that is indeed true, why do you think that’s the case.
My explanation is that philosophers sees too much, and thus can not live with the blind.
Maybe philosophy is better than sex.
Most of them arn’t that good looking, that might have someting to do with it. Thinking of Nietzsche, Sartre and Socratres. Although the last 2 had relationships.
I dont think that what you say is quite correct. Sexuality is a natural function of humanity and any deanial leads to situations like that in the Catholic church i.e. hypocrisy. I think that even the people who are celibate are either in furious denial or we dont know the full story. Of course there are people who are celibate, but i dont think that there is an especialy higher proportion among philosophers.
As Nietzsche says “Chastity is a virtue in some, but a vice in many” (Actualy i should include the whole chapter here (On Chastity, Zarathustra))
Not everyone is into looks.
I don’t believe you can compare philosophy to sex in a direct manner. Philosophy is generally about reason and intellect, while sex is about emotions and desires. Its like comparing the proverbial apples and oranges.
Why not have both?
But it helps
Well, for all we know these said philosophers were hitting it up every night. But for sake of argument we will say they were not. Perhaps because some were religious. Or maybe they had such a grandiose view of themselves they could never find a good enough mate to ever meet their requirments.
As for philosophy being better then sex…why choose one over the other if you can have both.
Being a man I can only experience one sexual orgasm an hour, if I’m lucky, or using a little blue pill. While an intellectual orgasms are multiple and can on for hour, days or even in some cases weeks! There’s no comparison! Philosophy floats my boat to higher peaks of ecstasy then the horizontal tango.
That many philosophers didn’t have visible partnerships doesn’t mean they weren’t sexually active. They may have practiced masturbation.
In fact, if you think about it, they may have had the best of all possible worlds; Physical and mental masturbation! 
JT
I disagree, there were many sexually active philosophers, like Schopenhauer, Camus, Foucault, etc.