Honestly, this is something that intrigues me. There are times when I'm editing video and I think: "How can a person this ticklish, endure so much tickling, so willingly, when they don't officially have this kink????" It's pretty much why I ask the question "What goes through your mind on the way to a tickling shoot" in interviews. Obviously, the pay is a draw - there are maybe 2 I've worked with who would just love to be tickled period though. The ones who state they hate it, have ultimately always admitted "hate"/"torture" weren't exactly the most accurate word(s). The following in no particular order are the reasons I've hypothesized after years (**These apply to models who specifically are not "INTO" tickling, or any type of BDSM predilection**).
1. Again, obviously pay.
2. Fun. There are some who really think it's just FUN. Not erotic or a turn on or anything, just pure fun.
3. Conditioning. Some are SO USED to being tickled silly by everyone around them, THEY don't understand how they can get money for it!
4. It's just another gig. Like being in a bikini in 40degree weather, or holding a painful pose over and over, etc. They don't see it any differently than any other hurdle they may have to overcome for the success of the shoot.
5. Catharsis. Tya used to say she had to make sure she had a very serious day (or days prior to the shoot), because she would be able to release all of those stresses. Several talk about how happy and "light" they feel afterwards.
I'm sure there are others. One thing I've discovered is how personal people's relationship with being tickled can be thus how varied their reasons for loving/hating/feeling indifferent can be.