I cannot let this explanation stand as it is. Attach rate drops with higher install base. The reason for this is simply, that a higher install base comes from different people buying into the system. You only have platformer fans? You get a WiiU. But that also leads to pretty high attach rates, as most of the install base share the same preferences and if you get a good game for that, pretty much every one owning the system buys that.
Every system goes through a phase like that. And that is launch. At launch you don't have a broad diverse spectrum of games, you have only so much. That leads to Breath of the Wild having nearly a 100% attach rate at the beginning. That dropped as the Switch base diversified.
PS5 not having this (in Japan) probably means that no title is a system seller there. Which is in line with the bad sales.
I thought I mentioned it, but after re-reading, that bit seemingly got lost during editing. So yeah at launch a system seller often has a huge attach rate (remember BotW reaching over 100% attach rate?), and there simply seemingly ain't anything big enough that launch.
That being said, even then reaching over 30% attach rate is very difficult even at launch. I did take the launch into account, but that part went poof. Both Sony and Microsoft tend to lack a true system seller at launch and rather launch with lots of fancy third party titles and smaller exclusives. As a result of this, unless one of the third party launch titles is a huge hit (think FF7R, a Dragon Quest or Monster Hunter title, for example), they simply can't reach high enough to chart.
The Nintendo eShop rating Thread: http://gamrconnect.vgchartz.com/thread.php?id=237454
The Steam/GOG key gifting thread: https://gamrconnect.vgchartz.com/thread/242024/the-steamgog-key-gifting-thread/1/