But the series doesn't have a bad sales history,its just unremarkable placed next to such big IPs that defined gaming
This is what I meant.
I don’t think Nintendo makes that much money on individual Metroid games, apart from a few exceptions. They couldn’t carry a system. They make enough to make making them worthwhile, and there will always be Nintendo owners who will buy a Metroid game.
BUT there is a certain segment of people will only buy in to a Nintendo system for a Metroid game, OR will only respect a Nintendo system with a Metroid game. And once the foot is in the door, people will naturally buy Mario Kart etc. I think this is the true value of Metroid.
On a side note, Mario Kart 8 is really interesting. It released on the WiiU, but nobody bought a WiiU for Mario Kart. Everyone bought a Switch for Zelda, and now Mario Kart is unstoppable.
Meaning people will not buy a system for Mario Kart, but they will buy it if they buy the system.