Wow...I haven’t heard any off the wall reasons but I’ll give you my standards. You’ve piqued my curiosity and I want to know what she said!
Mine:
"I can’t swim"
"I’m claustrophobic [and wearing all that gear underwater will make it worse]."
"I’m broke."
"We’re landlocked and won’t be able to do it often enough for it to be worthwhile." (from my midwestern friends)