[Dirlewanger]

A combination of things you mentioned and more:

* US has been suffering from its postwar boom period hangover for over 40 years now. The job market isn't like it was due to other emerging economies now having their boom periods. All those dreams and aspirations that millennials were promised (You can be whatever you want! Follow your passion and the work will follow) were shattered and turned out to be contemptible lies perpetuated by the secondary education system and the job market as a whole. As a result, a whole generation is saddled with debt, and are delaying milestones of life progression (buying a house, having kids), indefinitely for many.

* The rise of the Internet and the millennials being at its forefront has opened up massive new markets in the entertainment section, most notably Disney. They own most entertainment IPs, and know that millennials want to relive their childhoods so they sell it back to them. Comic book movies aren't just a fad like 80s actions movies were; they're here to stay. And Disney wants adults to keep being obsessed with what are essentially children's movies. All the social media companies want you on their product all the time using it and sharing everything you can (especially the juicy controversial stuff that is polarizing the country, oh boy do they love those articles).