Yeah I've noticed the same.

My current car (a Kia) was 9 months old when I bought it, and it had already lost something like 35% of its value.

My first car (a Ford Fiesta) was even worse - something like 40% depreciation when I bought it second hand (less than a year old too).

I'm not sure if it'll be a bubble (or at least one that'll burst), mind - plenty of people will only buy new, and usually on "risk free" PCP finance - and then keep trading in their car every 3 years. So whilst there's a good supply of cut-price second hand cars, there's also still plenty of new cars being sold as people stay on the PCP hamster wheel.