If Nintendo released Mario Kart or Smash Bros every year, I would stop buying them. One of the many great things about those two franchises is that they only come around once per console cycle. They go all in and make the best possible version they can, every time. You know what you're getting is going to be amazing, and that you'll be playing it for literally years.
Nintendo couldn't possibly, at all, make a full Smash Bros every year. It takes hundreds of people two to three years.
Nintendo is smart. Annualized franchises are horrible.
But they do it for Pokemon though and Mario in general.
No, not at all. A Mario series has never gotten an annual release. There are multiple, seperate teams at Nintendo that are in charge of different types of Mario games. The only similarity being that the Mario character is in them.
Pokemon as a brand may see nearly an annual release, but it's the same deal there. There's Mystery Dungeon, eShop spin-offs, and remakes in between main entries in the core series. There are at least two years in between main Pokemon core released, and usually three. As with Mario, there hasn't been a full 3D release since 2013.