Here's my explanation: some of us, including me are no longer just tickle fetishists and became tickle industry fetishists. I fantasize about both: tickling someone, which I do in real life, and about seeing girls, who are not necessarily aroused by tickling, get filmed while being tickled, for money or as an adventure. Somehow it is a huge turn on to me just to think about their emotions, personality and motivation to submit themselves to tickle torture. And the more complex these are, the more fascinqting it is! And what is more complex than a mature woman showing up for a shoot with her 20-something daughter, to star a video which is, at least, kinky.
Also, I once wrote a story about a fitness club where women worked out by being tickle tortured to their limits. One of the characters had her mother come visit her and watch her very first training session. Eventually, the mother reluctantly submits herself to the torture as well, demonstrating curiosity and some kind of solidarity with her child. They end up enjoying themselves but there is no room for sexuality there.
Obviously the tickle-industry part of the fetish is not something that I practice in real life. It is merely a fantasy which, as long as I don't set up my own tickling company, wil only remain that. Seeing a friend of mine tickling her mother and get aroused by that, I would turn around and walk away. But seeing them come for a torture session together, knowing that this is not a sexual thing for them, would be an extreme turn on to me.