It's a very common pattern too.

I don't find it strange that XMR is usually at the top or just right under (and in this example completely dominates, but if I understood correctly, this is for a single day, so it could vary a lot by day), but I find it incredibly puzzingly that seemingly even most bitcoiners don't use Lightning.

As you said, not large sums, so Lightning is the right fit there for at least two good reasons (lower fees, better privacy).

So yeah.. puzzling indeed. Is it possible most of those people paying with Bitcoin just don't realize how exposed they are paying onchain? Or don't care? Or don't know about Lightning?