Those things still exist, they're just reserved for completionists now. The optional content in any current era Mario game is arguably more awkwardly designed

Those things still exist, they're just reserved for completionists now. The optional content in any current era Mario game is arguably more awkwardly designed than anything from similar games in the NES era, with the assumption being that anyone attempting it is the kind of person who liked the 'Nintendo Hard' titles of the 80s. Presumably, designers now often see the 'main' adventure or campaign as for everyone, the multiplayer mode as a way to keep most people playing instead of fake difficulty and the 100% completion 'optional' content as for the masochists.