There are tons of dedicated porting houses so it doesn't have to take much staff or resources from the source company at all, and clearly it is worth doing as we're in the Switch's 4th year now and we're still getting releases like Immortals Fenyx Rising, Outer Worlds, Ori & the Will of the Wisps, Sniper Elite 4, Doom Eternal, Crysis Remastered, Subnautica, World War Z, Atelier Ryza 2, etc plus full-on new exclusives upcoming like Monster Hunter Rise, MH Stories 2, Bravely Default II, Rune Factory 5, Shin Megami Tensei 5, etc.
If the myth that Switch owners don't buy third party games was true, then it'd be in the same position now as Wii U was in 2015/16 with no noteworthy third party support at all.
What's the release date on Doom Eternal? I didn't think it had one. Good to see late ports either way, I guess. Better late than never.
Otherwise, yeah, Atelier games were on 3DS. MegaTen games were on 3DS. Monster Hunter was on 3DS. Bravely Default was on 3DS. Rune Factory was on 3DS. So the Switch has more third party titles than the Wii U because there is no 3DS. The Switch is all there is.