Pyro as Bill said:
Wii Fit was #6 and #7 on Wii, Ring Fit would be #6 on Switch if it didn't have to compete with Pokemon, Animal Crossing and a real Zelda like Wii Fit. It's the biggest new IP of the gen so far and the 9th biggest IP on the system. Despite being a new IP and not having a portable mode it's still sold more than nearly every Pokemon game. Switch Sports is Nintendo's biggest sports game dwarfing Mario Golf, Tennis and ARMS. They'll probably be the biggest new IPs of the gen taking 9th and 10th spot overall and they'd be even higher if you ignore software sales from the Lite and removed handheld mode for every other game. |
There's also a thing called the pandemic that shut down every gym on the planet and caused all fitness related products to skyrocket in demand, I don't think it would have those numbers without the pandemic occurring. Even basic barbells and weight benches were sold out on Amazon and in stores, Peloton stock went through the roof, etc. etc.