The software community is set up so that there is social compensation for open source labour. To a certain extent, the community of authors is the same way. The publishing community is certainly not set up so people are used to recogizing publishers for their contributions.
And some in the past tried charging for the result (rather than charging for support instead or as well, as RedHat and their ilk do).
It didn't work of course, but due to user education [the sort of people looking for Linux know they are likely to be able to get the same thing or better for free (plus media/transmission costs where relevant) elsewhere] rather than because it is wrong legally speaking, copyright or otherwise.