Id say I don’t believe they ain’t got fetishes. Some just hide that stuff bc it’s taboo but I think most of us have them. There can be several reasons for it too like respect not to cross the line and stuff. Usually there’s a trust element first and then that stuffs shared though. We try hard to not screw up too some times. It’s all just social pressure of doing the right thing. Truth is we fail at that too though it’s all just a struggle 😅
Shyness, insecurity? Negative past experiences in expressing sexuality with past partners? There can be multiple reasons, but it's something they should actively work on improving, if they have trouble with it