When you buy a used car, even one that's less than a year old, you have no way of knowing if there's something wrong with it. So buyers offer lower prices. Then a seller who has a car that they know is good says "I'm not selling it for such a low price, I know it's worth more." So the only people who sell used cars are the ones where something is wrong with them. A kind of race to the bottom.
I wonder how much this is affected by the prevalence of leasing. Something like 1/3 of new cars in the UK start off as leases. At the end of the lease period most/all of them hit the second hand market. In this case I think even the seller doesn't know if it's a lemon or not and, in any case, they will always want to liquidate the car as soon as possible, even if it's a peach. So they would factor the market price into the lease deal and sell all cars at market price regardless.
Concerns over reliability? Some car issues can be erratic and you may not find out about them until some time later. If you buy used, there's a level of risk regarding what the car's been through with previous owners. If you have a family and/or work with a tight schedule and/or park in areas where you wouldn't like to be left stranded, you may really value reliability.
You've never heard of a brand new car going wrong? A used car that's been on the road for 10 years with a full maintenance history gives me more hope for reliability than a brand new car that hasn't had time to reveal its problems. You can always pay someone to insure you against unlikely events and they don't care at all whether the car is new or not. It's up to you to decide how much risk you want to take.
I think for buying reliable cars, new is the way to go. They cost way too much used and the first person got all the best miles out of it. Unreliable/niche cars, used all day.
>that depreciates by 30% the very second you drive off the dealership
Nobody would underwrite loans for new cars with low down payment and low interest if this had been true. Also we would see the year old cars with low mileage selling with >30% discount, which is also not the case.
The reason I buy new cars is customization: I get exactly the car I want with colors/materials/options I selected.
When you buy a used car, even one that's less than a year old, you have no way of knowing if there's something wrong with it. So buyers offer lower prices. Then a seller who has a car that they know is good says "I'm not selling it for such a low price, I know it's worth more." So the only people who sell used cars are the ones where something is wrong with them. A kind of race to the bottom.