Splatoon 2 is a terrible fucking example so i don't think you thought this through. The game was barebones as fuck at launch and will stop receiving content updates way,way,way before Overwatch does. Not to mention Nintendo have a console to sell so they need to sunk costs to make it more appealing.
Nintendo games also tend to have evergreen sales that's pretty unique in the industry. Not to say other games can't sell the same way; GTA5 continues to sell like crazy at full price despite it's age; but Nintendo games have much higher sales 2 or 3 years after launch than most games do 2 or 3 years after launch, and those sales are still typically at full price unlike other games which typically are highly discounted at that point.