Why would that be? Obviously, the lack of supplements post-Essentials was due to resources being diverted to developing 5e (as well as resources just plain being slashed when D&D failed to meet unrealistic revenue goals, of course). Once 5e is in the can, shouldn't WotC be able to churn out new material at a reasonable clip?
I think you have to differentiate between the brand and the game. 'Dungeons & Dragons' will probably always be THE thing people think about when they think of role-playing games. But to amateurs, Pathfinder is D&D. So is 13th Age. So are various OSR clones.The pie analogy doesn't quite work, because it leaves out the issue of player acquisition - something traditionally done by the leading RPG in the industry. D&D is the only mainstream brand the industry has of its own (no matter what the difference in sales between the leading games are), and WotC is in a position to leverage that to grow the industry in ways that other companies can't, although Paizo has made some inroads into that with its Beginner Box and various branding initiatives like comic books, toys, and so on. So a successful D&D means a bigger RPG industry with more players in it.
Plus, of course, actual competition makes people bring their A-Game. Neither company can coast. This benefits everybody!
Paizo will thrive, and if 5E takes off I would not be surprised to see them absorbed into Hasbro / WoTC.
Lisa Stevens (and plenty of other Paizo staff) came from WotC. I don't want to speak for them, but I don't imagine for a second that they want to go back. They're doing what they want to do, the way they want to do it.
If Hasbro bought Paizo, I doubt the staff would have much of a choice.
I think you have to differentiate between the brand and the game. 'Dungeons & Dragons' will probably always be THE thing people think about when they think of role-playing games. But to amateurs, Pathfinder is D&D. So is 13th Age. So are various OSR clones.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.