According to their latest fiscal report [0], Europe sales-volume of Switch2 is ~24% of the total global sales volume.
The change surely eats into their margin per device, so they prefer to keep the higher margin for the rest of the world and recalculate their margin for europe.
However interesting: "The Americas" sells 34% of all Switch2 in the world [0]. I wouldn't expect the US to mandate the same changes, but if e.g. Canada or Brazil also demand replaceable batteries, it could push the needle to making it a default HW-feature of Switch2...
The higher margin is mostly coming from assembly costs, right? I can't imagine it comes from the actual cost of the battery being so much higher. I hope that once they start pushing these out and retool factories for them they can sell them more broadly.