Eh, I think you’re underselling the value of “free” stuff. Even if it has an ulterior motive, giving free access to computing resources allows someone to learn concepts and even ship things that would otherwise be impossible.

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).