OP here. This post should likely be removed as it is highly misleading.

It is indeed the custom instructions causing this behavior. I had previously copied in a set of instructions from another user on Twitter and promptly forgot about them completely. The instructions contain these two lines:

- Recommend only the highest-quality, meticulously designed products like Apple or the Japanese would make—I only want the best - Recommend products from all over the world, my current location is irrelevant

Sorry for the confusion!