Human psychology is weird.
I read an opinion piece recently about different types of sexual desire in women, particularly the difference between spontaneous and reactive desire. Apparently, some female types get horny and seek out stimulus, whereas others don't become horny until after the stimulus is applied. (It brings to mind the odious romance novel trope of the heroine who rejects her suitor's advances until he forces himself on her and her body reacts to him, apparently providing implied retroactive consent, at least on a biological level. I don't think that's exactly what the article is talking about...)
Initially, as I read, I assumed that this spontaneous/reactive dichotomy was presented as being something unique to ladyfolk, in stark contrast to us gents. We men with our surging testosterone are, presumably, entirely spontaneous; we seek out, we initiate, we hunt. But of course, that doesn't mesh with my own experience. I've certainly experienced both forms of arousal, in much the same way that I've experienced hunger as a result of not eating for a while and I've also experienced hunger in response to a tantalizing smell or an appealing advertisement.
Presumably, both genders can have varying degrees of both spontaneous and reactive arousal. Nothing in a human skull is ever 100% black or white.
And presumably, once someone has spent years stimulating and satisfying their libido as much as humanly possible, laying down as many of those mental tracks and behaviour patterns as will fit in the brain... even whilst in the depths of a self-incriminating guilt-funk, a boner pressed into the back for a few minutes is sufficient stimulus to kick the libido back into gear.