Of course it will depend on the publisher, even if the system was discontinued. A lot of games releasing for PS4 and X1 are missing Switch even if Switch is rapidly approaching X1 LTD.
If they don't see a reason to port now, they will see even less when they start making PS5/X4 games, even if they port to the discontinued consoles.
With 4 year development cycles, it's not a surprise that Switch isn't getting third party parity yet.
A big game releasing today would have began when the Wii U had a global install base of less than 9 million units. How do you predict that by launch date that Nintendo would have a successor console out selling like mad?
Switch is already on the market for 2 years (and dev kits, and specs probably nearing 3 years have been know unless Nintendo have just ignored 3rd parties). And we have heard from a lot of people and fans that it is very easy to port to. So there have been plenty of time to do porting and launch together.
And I wasn't even saying they aren't seeing a reason or criticizing the quantity of ports. I'm saying that for games they don't currently see a reason they won't see in the future.
Games take 4 years to make, but still we see plenty of games at launch.