What "complicated" about MH Rise and Momotaro?
The former is an entry in a franchise that's more popular any oxygen in Japan, so it sells like crack. Seems pretty simple to me.
Momotaro is a series that's traditionally popular on home systems and as this is the first one in a while that can be played on TV, it sells like crack.
Neither seems like an alignment of the stars or lightning in a bottle to me, just historically popular franchises selling well on Switch.
No Momotaro game ever sold over a million copies before and now the newest entry is outselling the previously best-selling entry by over 3 to 1 and is Konami's best-selling game ever in Japan.
Since it looks like the next Yu-Gi-Oh game is also going to be massively popular I guess it's just the Switch, but if that game sell 2mil copies it would just mean it's back to it's previous highpoint, but in Momtaro's case that's a massive overperformance.