In an unrealistic pipedream, Nintendo would have unlimited amount of competent employees being paid with huge amounts of money, and able to create a shitton of great games to all their available franchises (and I mean all even including very obscure ones such as say, Joy Mech Fight) and in that perfect world today we'd probably get like Metroid Prime 8 and maybe its 5th spinoff.
Realistically in the end Nintendo is just a game company and they are doing what they think gives profits to the company. There's tons of new games which are in development right now for Nintendo (which I hate that this obvious fact has to be brought up), and it also doesn't help that nowadays some of the stuff Nintendo put out are in incomplete states to be later fixed with free updates (looking at you, Mario spinoff games on the Nintendo Switch), and when you take all of this into account I don't know why these fanboys act as if Nintendo is ignoring them when there's so much shit going on and this is something not as simple as its fix being "just hire more staff".
Besides, Nintendo has been reviving some franchises here and there like giving remasters to some franchises like Advance Wars and even Famicom Detective Club and I don't even know why Metroid is brought into this conversation especially that we got the Metroid Samus Returns remake on the 3DS and Metroid Dread.