Bella,
For me: when enjoying a */F tickling clip, then it's all about drinking in the girl's expressions, her features, her laughter, her beauty, while she's being caused to display them all. It's largely just because it's just sexy.
On the other hand, I've found F/M clips to be extremely exciting too, if they're done well... but it's completely different. Two completely different moods.
For me, when watching F/M clips, it has nothing to do with the particular man being played with. It's about its ability to immerse me in the thought of my own erotic vulnerabilities as a man, and the ease with which a woman can exploit them if she's talented. (For that reason, the quality of an F/M clip is determined by the talent of the "F".)
The sexual content is the same at the core, and it's again based on the woman's ability to take him over. Consider that women can be aroused and, if they're trying to do so, hide it fairly well. Even a female orgasm, to a bystander, is mainly indicated by the way their bodies and voices move, and they can potentially hide it if they're trying. Conversely, women can also fake orgasms.
On the other hand, a naked and restrained man can neither hide sexual arousal nor fake it, because of the (blatant) erectile process. When orgasm is in question, men can neither create a fake orgasm, nor hide an authentic one, because of the (even more obvious, and when it's triggered, completely uncontrollable) ejaculatory process. Unlike the many other opportunities for men to mislead, protect or conceal their sexual feelings, his sexual processes completely bypass any mental defense mechanisms and present a completely honest response to the woman, even if he's actively attempting to prevent it. (Not to be ignored are the intense physical and emotional sensations that any male viewer will understand full well she's putting him through.)
Even if he's trying to be strong, a good tickler can <I>make</I> him laugh and dance. Even if he's trying to project that he isn't affected by the sexual power of women, a talented woman can <I>make</I> him get an erection and ejaculate. So, at the core, one of the reasons that I think some men find tickling so erotic is the <I>same</I> reason they find being helpless and stimulated erotic. Clips that embody that reason are the ones those men will love.
... Does that make any sense?