Batteries losing more than 20-25% of their capacity in 150.000km had a defect in production already. You can find similiar numbers in any OEM's warranty. So a non-defective battery will provide at least 80% of its capacity at 150.000km. The average car manages about 250.000km over their life-time of about 15 years (reference numbers from the US, so the most pessimistic view as barely anyone else in the world is matching those distances).

You are not completely wrong. Used batteries will be a problem... somewhere far down the road because electric vehicles are expected to easily manage 800.000km or more (less moving/wear parts).

But we are not there yet. The whole EV market isn't old enough to have produced these long-lived vehicles and we are back at my original point. Today it's not about battery degradation but about EVs not getting old fast enough to already have established a robust used market. In fact the first big batch of EVs on the used market is often not expected for another 2 years (see here for example, and that's again rather new vehicles because of a loophole for leased cars in the EU).

In short: There isn't a huge used EV market yet and (more importantly) the demand is stifled by battery degradation fairy tales not relevant (EVs old enough for this basically don't exist yet) and political mismanagement subsidising new EVs.