Perhaps, but it reduces the size of the secondary market so consumers have less choice and may opt for a new one instead. This is the real advantage to Apple.

Is there a secondary market for a ten-year-old MacBook Air?

I use a nine-year-old Air almost daily, but I don't think the vast majority of people would consider it viable, let alone pay for one.

The silver lining of the "Apple Tax" is that machines retain value for an absurdly long time, even those which are verging on "obsolete".

Ebay shows a load being sold for between £70 and £120. Here's one that has actual bids on it. (£106 when I post this comment). https://www.ebay.co.uk/itm/Apple-MacBook-Air-13-inch-Late-20...

If it can install latest macOS, it's a good test machine to test the newest OS to see if it sucks or not.

It's certainly to the same type of people who would buy a new product for 5x the price instead.

Exactly. Same reason why they offer free engravings.

There's no meaningful competition between new Apple products and ten-year-old Apple products.

But if you want to talk about much newer machines, Apple doesn't offer good trade-in prices, so it still doesn't look like they are trying to beat out the secondary market.

I think it's pretty clear the trade-in offers are a convenience they can provide more than anything.