Resale value of the older laptops is still decent. 2013 MacBook Pro’s still going for £750 on eBay - For a machine 8 years old? I think it only cost £2000 back then anyway. So that Mac has only cost £13 a month to own.
In the US market there are some power sellers who say 2 year warranty and get big prices. Meanwhile while I was selling 1 as a non-prof seller I got tons of questions of "can I return it" and "what is the warranty" and two times my item was bid up to the stratosphere by non paying biders. Finally I listed it buy it now only and eventually a no fuss buyer bought it for half the price of the prof-sellers.
My point is, ebay prices don't always tell the whole story.
Here's the £850 one - does have a TB SSD but still...
https://www.ebay.co.uk/itm/apple-macbook-pro-retina-15-4-Inc...
And the £620 with 256GB https://www.ebay.co.uk/itm/Apple-Macbook-Pro-15-inch-mid-201...
That is some serious value being retained right there.
Saying that, I still own a MacBook Pro 2013 and a newer 2016 for from work, and the performance is indistinguishable - so maybe £750 is a good deal.
That is all part of the reason prices stayed high - until there was a genuine update.