Some people like to be useful in general. Others enjoy their craft, do it for fun, and make it available to the public in a nice way. Another reason could be

Some people like to be useful in general. Others enjoy their craft, do it for fun, and make it available to the public in a nice way. Another reason could be that it also provides advertisement for the person providing the work. The 'money for free' angle is very strange to me : a lot of things provide value, it's not a bad thing to provide something for free, even if companies can use it as well.