I suspect it costs even more to extract the small amounts of REE from scrap electronics than it does to extract REE from Bayan Obo ore.

Recycling is hard. Particularly in comparison to processing ore. When reclaiming desirable metals from electronics you are faced with an extremely heterogeneous starting material - sheet metal cases, fasteners, glass, all sorts of plastics, fibreglass circuit boards, insulated wire, etc.

In contrast, REE ore is a relatively homogeneous mix of silicates, oxides and carbonates. All are inorganic, and have sufficiently similar properties that the bulk material can be crushed then milled to a fine powder ready for processing. If your resource is competently characterised, you will also know to a reasonable degree the REE content to expect per tonne of ore.

What is the Nd content of one tonne of e-waste? Hell, what is the composition of 1 tonne of e-waste? How do you even assay e-waste?

Presumably, since they're actually fairly common, and not rare at all, extracting them from the surface of a smartphone is no easier than extracting them from dirt itself.