Cause Nintendo doesn't make annual franchises (except Pokemonsh) and that is how they make money. Games like Mario Kart, SSB, WWHD, DK and etc come like once a generation and this is how they can make the most money out of them cause they know that people that want them would buy them regardless
PC Specs: CPU: 7800X3D || GPU: Strix 4090 || RAM: 32GB DDR5 6000 || Main SSD: WD 2TB SN850