Tabletop gaming as a whole is hugely popular right now. Not just DnD but also boardgames/cardgames/etc. I give a lot of credit to the massive surge in gaming popularity to the recession of 2009. When it got expensive to go out and have fun lots of people holed up at their house and started playing board/card games as an alternative. This wave of popularity led to the gaming online series Tabletop with Wil Wheaton who had a huge impact on "regular people" getting into the gaming hobby.I think 5E biggest factors for success are.
1. It's reasonably single
2. Mature social media that's positive
I think 5e had the great timing to redesign itself to be accessible at JUST the right time that a lot of people who would have been uninterested in it instead gave it a shot because a friend played.
It also helps that younger adults are more likely to see board/card/rpg gaming as something "fun" not "wierd" because of the general popularly of videogaming