If WotC hadn't been bought by Hasbro, who knows. But look at it from Hasbro's perspective. They've got the top name-brand recognition IP in fantasy gaming, in roleplaying in general. Is this giving them more traction or are they losing ground in the market? That analysis is embarrassing. If Hasbro spends the money to come out with a new line of Transformers and the new line creates a surge in Go-Bots sales? There would be some people in serious trouble. The fact that WotC is a separate division is probably the main reason they are even getting to try again.
Now, picture what happens if 5E not only unites the customer base (as much as within reason, at least) but also creates a resurgence? New players come on board? Well, that will lead to a jumping off point for more licensing uses for the brand. A D&D movie reboot. Lunch boxes. A toy line. These are the things a marketer pictures, to take the brand to a point where you earn much more money from incidentals because, really, just how many 500-page books can you reasonably sell?
What Hasbro wants is to cash in on the kind of attention you see in My Little Pony, which is a cultural phenomenon, or Harry Potter, which pretty much defines a generation. It's a good time to do it, too, as fantasy is on the rise in the modern consciousness. I mean, really, we aren't exactly seeing a lot more On Golden Pond and Chariots of Fire today. We're seeing Lord of the Rings and Captain America.
If 5E fails? Well, TSR failed and somebody eventually bought the rights when it wasn't worth much. So...
Thinking about superheroes, I wonder who owns the rights for the Marvel Superhero game? TSR put it out, but it obviously traded heavily on the Marvel name. Does anyone remember if WotC bought out all of TSR or just the D&D rights alone? They must've bought out TSR, they put out Gamma World again.