It's on 3 platforms, higher prices but also higher development costs. WW the 3DS games ranged between 4-5m which is on par with what MHW sold on each platform WW.
The 3 multiplatforms did not cost nearly as much as 3 single platform PS4 exclusives would, so in reality it is quite cheap to port it to systems with similar specs and architecture. WW the 3DS games did not pass 4.3m. Without counting Iceborne, MHW sold 15.7m a 3.65 multiplier of the highest 3DS entry. With Iceborne it is 20.9m, a 4.86 multiplier.
It really isn't comparable.
Dead or Alive 6, they kinda f$&@&$ up the marketing trying to make it a serious fighting game (before sorta coming back the T&A) and pricing their costume Season Passes at ridiculous prices.
Dynasty Warriors and Romance, I don’t know what happened to those games. They attempted to do something different and it backfired on them, not to mention the bugs from DW.
Weirdly enough, their Switch exclusives (FE:W, HW:DE, and FE:TH) did reasonably well in Japan, I believe.
Koei Tecmo has shown great support for the Switch, so I don't see why they would drop support for no reason.
DW9 had massive issues on release and in development on the main platforms, I can only imagine porting it to Switch would have not been an easy task.
Dead or Alive 6 not getting more ports didn't make much sense after how well they did with free to play.
Romance, like I said they must have had a reason for dropping Switch and XB, while only keeping PS4 and PC. It is not a high selling game, so the difference in sales definitely matter.