content: I think it's two things: to reward already existing users with a free upgrade, and to still maintain their business model. Pirates are going to pirate anyway, so there's no reason to reward them. Very few people buy Windows, so they just stick on the old version they've got (I just encountered XP on my bosses' old laptop). Giving away Win10 to existing users means more people will remain invested in that ecosystem, which gives MS money, especially for Office and the Windows Store. That said, they still want to sell the software. It might not cost $120 like it used to, but it's certainly not free. If they truly didn't care about selling a Windows license, then Windows 10 would just be free forever, not for the first years for existing customers and also pirates.