I think this is because, 'If I'm not gaining anything, you shouldn't either' attitude.
Programmers would be pissed if the code written by them gets used by somebody else to make money, while they don't make any money out of it. Isn't this the whole Java debate these days all about. Sun/Oracle aren't getting much money out of Java(While writing/maintaining/advertising it) while the whole world is using it to make money.