>>64837
I have a few theories.
The fact that she's emotionless may actually be a draw. People love tickling characters who generally don't express very strong emotions because we want to see them in a situation they're not normally in. These pictures you've shared where she's openly laughing makes her almost look like a wholly different character from the calm and composed trainer we normally see, and seeing that shift in disposition from "our" fingertips has a strong appeal.
I also think it's because she's a trainer, there's a bit of a power play dynamic going on. The assumption is that you're paying her to train you, and she's kind of calling the shots. She's the expert, she's the one spending her time being here helping you get in shape. Being able to reach out and tickle her foot and bring her down to "your level" is very appealing. It's like the old "teacher tickled by her students" fantasy, you want to feel like you're in charge for a bit. Maybe you want just a little bit extra in the exchange of money and time, or maybe there's just a bit of weird appeal in paying someone to do something and then tickling them while they do it, making it much harder for your own pleasure.
A lot of this is also assuming a private trainer, but this could also wrap into public tickling scenarios if she's just leading a class. Then you have a whole bunch of people reaching forward to pull her down, hold her still, and tickle her senseless, and anyone walking by can just join the fun. That's appealing too.
This may be specific to me but I have a bit of a thing for women calmly and matter of factly telling me to do fetishy things for them. Like that picture BadCrab did where she's "speaking" in her usual measured tone but it's all stuff like "get on your knees and worship my feet. Drag your tongue from my heels up to my toes, and make sure you cover every inch", like she's just instructing me on how to do something kinky like it's an instructional video. I don't know why but there's something to that that holds an appeal.
Plus, you know, fit toned woman. Good to tickle. See how long she can hold her pose while I tickle her toes. If she's gonna have her feet in my face the whole lesson I'm gonna get something out of it myself. I thought I only had like two ideas but I kept getting more as I wrote this so hopefully I don't sound obsessive.