Google did not do this out of the goodness of their heart. They did it to lock you in with Firebase, Maps, etc. And believe me, the moment they start charging you for it, you quickly realize why Google is not a company to give an ounce of trust to.
None of these companies are altruistic and everyone knows it, but by not charging upfront it gives possibilities for millions of developers who don’t have US$ 50/month to spend on something (students, emerging economies, career changers, etc).
There's a lot of transferable skills gained in these products. You're not just operating a Maytag.
After all, why care? It's not like those people were gonna buy it anyway, and they're still using windows, aren't they?