this is sad

> I've seen all kinds.

Then you are in luck.
I've never seen any other then maybe Netbooks in physical stores and online stores still fail to offer Linux as an OS option.

> Dell is still selling Linux laptops

They started recently with single models for which reports often say that things don't actually work and official blogs telling about workarounds or making promises of updates.
They have yet to actually offer Linux as an option on their machines for customers who buy computers based on requirements.

> The fact that it has never attracted more than a trace interest is notable.

We don't know, since there has never been any attempt in offering Linux as a pre-install option from any of the major vendors.
Only specialized vendors such as ZaReason or System76 do and they don't have widespread presence and only a limited range of models.

So far, whenever I needed to buy a new laptop, none of the vendors who's products met the requirements closely enough to get into the final consideration was able to offer the device without OS, let alone with Linux.

It is great if that is different in the place where you are from.