- Access to source code is not the primary concern for most people
- Having an option to work with the source code is important to few
- Few people who have access to the source code actually use it
- There is no "right" software development model.
- Much open source software has commercial interests.
Of course this list glosses over some other possibilities that might seem more viable if Microsoft had not illegally monopolized the software industry. People and corporations in the open source movement might prefer to market their software commercially at a fair price if there was fair competition. Investors might actually fund these ventures if they had confidence that there was some hope of a return.
I don't assume that all open source supporters are altruistic. They do seem to be realistic in today's software industry climate.