Because Islam forbids men from touching a woman who is not their wife/mother/daughter/sister/grandmother/grandaughter/aunty, or neice. And of course the same applies for women except for male relatives similar to above. Cousins are not included in this category. It is forbidden to shake hands with them let alone give massages. Islam closes the door to temptation. And if you’ve not heard of men feeling temptation from being massaged/touching women, then you need to educate yourself on the subject.
