Having to pay for every small nut and bolt is a deterrent from reuse, even if only because it is hardly manageable in a non-linear world. I guess this shows the difference between people who believe in money, like most modern economists, and people who believe in people. But no one is being paid when a theorem is used, and that is why we use them so freely for everyone's benefit. The only incentives are quality, recognition, personnal accomplishment and general welfare. The main advantage is that scientists, or free programmers, take the time to do things right, and to redo them.
Quality is the ultimate goal.
Industry, on the other hand, has all kind of strange constraints, like time to market, or doing it like the guy next door. Money is the ultimate goal. The main reason they buy some software is because others are buying it, even when they know it is not the best. The same holds with technological choices. But free programmers are free in many senses, including the freedom to chose the right solutions over the popular ones.