They do reuse their franchises but I feel the games (at least in some instances) are very different, for instance BotW is not same as Oot, they are same franchise, so share some lore, but practically speaking they are their own games.

As for Mario Kart, racing and fighting games work like that, unless a franchise flops or something, we keep getting more games every generation or so.

They did release couple of new IPs, like Astral Chain and Arms (and Ring fit and Labo, if we count those), but I do agree that there should be some new IPs.