I have so much to say on this topic I could write a novel, e.g about commercial artists versus those who just want their art to be seen versus art commissioned with money obtained elsewhere. But in the most simple terms, at least with me, is I prefer to write and to use software with as few restrictions on/from others as possible. Can't feed my family on that of course and wouldn't try. If public domain were more accepted than MIT, I'd do it, but for now I just slap MIT on it and move on. If you make a million dollars on it, keeping changes hidden or not, good for you. I'm trying to do the same in my day job, the primary code of which is of course closed.

As for the prevalence of restrictionless licenses on non-hobbyist software, you can attribute that to their stewards simply recognizing the value of hobbyists working with it (the company reputation gained, the influence, bug finding, etc). People want fewer restrictions, companies want people.

The gpl was always about end user freedom. The bsd/mit is more about developer freedom. Neither guarantees upstreaming of changes - but many see the gpl as effectively requiring publication of changes. And it does prevent restricting such publication.

But if you develop a point-of-sale system (say) and sell it to a store chain - they might not have any motivation to publish the source - even if it includes a patched mysql, or some gpl code etc (maybe a patched Linux kernel?).

Now, the client has the source, and hire someone else to adapt the system as needed, or publish the source if they want. But the gpl doesn't demand giving anything back to the original authors.

How is bsd different? In that case the pos could be delivered without any source code. The client wouldn't be able to maintain it without help from the original vendor.

They also have no obligation to publish it. You are distributing the software to them, you have to give them the source code along with it. They are using the software, not distributing it further, therefore GPL does not require them to publish the source code.

(I'm not trying to argue with you here, as I think you know this - I just thing your comment does not make this detail clear enough. :) )

Commerce is a fundamental fact of life and for many projects an opensource approach just doesn't work, this a lot of people have to opt for closed source for business reason, but the very same people would like to leverage libraries and "open software". I do. And this is why everything I publish publicly is under a permissive license.