everyone has a phone nowadays, I think the expectation that the e-waste cycle would continue was a misjudgement. For most normal people I know, windows 7 was their last "laptop generation"(10 at the latest) before they could have switched entirely to their phones or tablets. They also don't really bother getting rid of this gear by sale, most of the prior generation's machines were priced in the thousands and were towers so it made more sense to resell them, that generation(to my perception) was mostly thin plastic units with almost no durability. Most people I've seen hold onto them "just in case", as they wouldn't sell in their condition.

Perhaps it's getting repurposed?

Think about the demand and supply curves of calculations (or computation). For most of history, they moved in tandem, with supply moving slightly faster, so computers would always do more at slightly lower costs.

Now both curves are speeding up, but demand is moving faster, so the costs of hardware are going up. And when high end servers (with GPUs) are unavailable, people hold onto the older ones longer.