The reason isn't given, but I suspect NAND chip shortages & tariffs are to blame: Nintendo has announced that first-party Switch 2 titles will have a lower MSRP on the eShop than the physical release.
(Edit: We're talking about a discount on the eShop. Physical game prices aren't increasing.)
I've seen confirmation of this in Australia and the US. I think this was already a thing in the UK?

Nintendo clarifies Switch 2 pricing changes in new statement, says physical prices aren't going up
We have an update from Nintendo regarding the price changes for Switch 2 which should clarify the situation. In its announcement today, the company said that “new Nintendo published digital titles exclusive to Nintendo Switch 2 will have an MSRP that is different from physical versions.” Some were confused about what that actually meant. Essentially, what’s going on here is...