Don't have any stats for comparison between nations but I wonder if the UK has a bigger leasing market that releases a lot of 2-3 year old cars to the used market, driving down prices.
I am sure its lots of factors, that included.
Also factors:
Date number plates so people always want newer cars to show off
PCP - makes car buying new cars cheap and affordable.
Cars over 3 years need MOTs and higher running costs compared with new with warranties and sometimes services all included
Expensive insurance and veh tax and fuel duty means its expensive to run any car whether its a £2000 car or a £20k car.
RHD - smaller market for selling your used car to
Dealer discounts on new cars - before covid it was easy to get up to 20% off a new car, sometimes a lot more. I bought a brand new £65k list price VW touareg for £38k. Where does that put second hand values at for a one year old one? Less than £38k obviously.
so lots of factors.