They didn't. They're having a big spike, right now [1]. It's going to end up being bigger than the summer wave. They had a big spike last winter, too, but they weren't testing as much then.

Comparing the absolute magnitude of these spikes is fraught, because they depend on the number of tests being conducted, (which was rapidly increasing over the course of last year), as well as the many other behavioral changes that were happening at the same time.

[1] https://coronavirus.jhu.edu/region/japan