>>4339864Here's my own personal experience:
I've had a bondage fetish and foot fetish for as long as I can remember, even when growing up as a kid. Early on in exploring the vast reaches of the internet, I stumbled across a picture of Terra from Teen Titans in bondage, barefoot, and getting tickle tortured. I stared at this picture for a long while, wondering what it was about it that seemed...oddly appealing. And then it hit me:
Tickling can be a form of torture that leaves no physical damage to one's body. It can force reactions from the victim, making them laugh uncontrollably, wiggle and squirm. It can often involve a heavy focus on the feet, as this picture showed me, with the foot being exploited and explored by all manner of tools.
In short, it appealed to my fondness for bondage by virtue of providing a fun thing to put a captive through without actually harming them, AND can heavily involve the exploration of their feet all the while. It's an excuse to play with their feet for the purpose of messing with them in their state of helplessness.
After that day, tickle torture became my third favorite fetish. These days, thanks to tickling I've gotten more interested in different spots, like the navel and armpits, and I rather like upper body tickling in general. I still prefer seeing feet getting tickled, though, since my foot fetish is still in second place.