Well if we’re talking general third party support I’ll toss in my speculation.
IMO the problem with Nintendo when it comes to third parties, which is also their strength, is that Nintendo does what it wants when it wants. The PS4 and Xbox are basically the same console. I have to imagine developing a game that runs on both or can be ported from one to the other is a more straight forward affair.
At the same time when looking at the market that buys big third party games (“gamers”), it’s my guess that Nintendo consoles are usually a companion purchase. In other words the Nintendo console is probably paired with a PS4 or Xbox or PC. If that’s the case then those people are probably purchasing their big third party games on the more powerful system.
The curveball with the switch is its portability, which could lead people to purchase a big third party game there instead of for their Xbox or PC or PS4. Do the number of people that would do that make up for the time, money, and resources spent porting games over and making sure they run well enough? I dunno. It made sense for the Wii because it did stupid numbers. Time will tell for the Switch.