It's weird and they could definitely be selling around 5K per week if supply was there but to me with the reveal of the PS5 they've given up on Japan and now it's going to be an entirely Mobile + Nintendo dominated. This will have long term implications for the console business, as next year I don't expect PS5 to be able to achieve more than 15% market share in terms of hardware. Their succession of handheld gaming after the Vita failed due to lackluster support and losing Monster Hunter to Nintendo ended up starting to show ramifications very early in the Switch's life. Now we are starting to see the full effect, as even during the DS/Wii days the maximum market share Nintendo achieved was around 66% because PSP still had a lot of games you could not purchase elsewhere. Now with losing their portable franchises or unsuccessfully trying to migrate this audience to the PS4, their prior partners and supporters have three options - get on the AAA train, start supporting the Switch or go out of business.
We already saw that God Eater saw two declines from the PSP when it was selling >600K, on the PSV the top-selling game sold close to 400K and God Eater 3 on the PS4 managed a paltry >200K. From all their portable IPs, the only one we saw that saw growth was Persona and that was partly due to the larger scale and budget for Persona 5, which paid off leading to the best selling game in the franchise.
Sony is still a great partner for AAA, because you can be certain if your AAA game is exclusive to the system, Sony Japan will market the hell out of it.. but any developer unable to invest so much, it's a difficult value proposition - to risk it all on AAA game in order to release it on a console that would sell 10-20% of what the Switch has potential to sell in Japan could sink a studio. Even in Japan AAA budgets are no joke, especially for studios and publishers that are already in a risky situation because they didn't change their long term strategy to include multiplats for the Switch on their home turf.
Imagineer with a single game has sold >122K physical in Japan thus far(digital probably makes it much higher) and this is not a cheap game Fitness Boxing retails at ¥5.800. This is more sales than Atlus, FuRyu, Nippon Ichi, Idea Factory, Spike Chunsoft, Arc System, From Software etc. have sold on the system. It also continues to sell, much like Fishing Spirits & Taiko you can achieve evergreen status if you have a great concept and a company invests in marketing. There is a reason why Bandai has been doing advertisements for Fishing Spirits and Hori even released a peripheral for the game in Japan. Smaller more agile studios that were quick to jump on the Switch bandwagon with novel concepts will now reap the benefits while others still struggle to even find a 100K seller on the system.