So why not open source windows from the beginning and save billions, and a ton 'o precious programmer time?
Increasingly, corporations are concluding that investing in licenses for other's proprietary software is wasteful and they are seeking out open source software where they can, to avoid lock-in and network effects. So a hundred years from now, that may be the standard view of proprietary software. Long before that I hope we recognize how awkward applying artistic copyright to code is, and grant a four or seven year copyright, but only once the code has been revealed. The purpose of granting intellectual property rights was originally to create public goods, that's just not what's happening with computer code.
The GPL is commonly cited as the reason why Linux is where it is today. It's a different incentive model to be sure, but one that undeniably works. It's why many prominent projects continue to use it, and it's why new projects use it as well. The only thing the GPL slowed down is people who aren't willing to accept how the GPL was designed to work.
Sure, I'd love a world where copyright was laughed off and where DMCA and anti-circumvention laws were annulled (i.e code is treated like the math that it is), but that's not the world we live in. In this reality, I and many others believe that the GPL provides the best trade-offs in terms freedom to users (and thus developers).