A luxury saloon can lose a very large share of its value in its first few years, far more steeply than an ordinary car of the same age. The mechanism is about future costs rather than desirability.
Running costs are set by the original specification
Servicing, tyres, brakes, suspension components and electronics are priced according to what the car is, not what it is currently worth.
A set of tyres for a large luxury car costs the same whether the car is new or a decade old, and the same is true of an air suspension unit or a control module.
As the value falls, those fixed costs become enormous relative to the car, and at some point a single repair can approach the market value.
The buyer pool narrows at each stage
New luxury cars are bought largely on finance by buyers whose budget covers the payment comfortably. Those buyers replace the car at the end of the term.
The second owner is buying at a fraction of the price but inherits the full running cost, which requires a different and much smaller category of buyer.
Fewer bidders for a given car means a lower clearing price, and the effect compounds as the car ages and the required tolerance for cost rises.
Technology dates faster at the top of the market
Luxury cars introduce new systems first, which is part of their appeal when new and a liability afterwards, because the following generation renders them visibly old.
Infotainment ages fastest of all, since its interface and connectivity are compared directly against a phone that is replaced every few years.
Repairing or replacing those systems is rarely economic, so the car carries obsolete technology for the rest of its life.
Supply arrives in predictable waves
A large share of luxury cars enter the market through leasing and company schemes with similar terms, so they return to the used market in concentrated batches.
Those batches are heavily weighted towards the same specifications and colours, which increases direct competition between nearly identical cars.
Manufacturer incentives on new models pull the whole price ladder down as well, since a discounted new car sets the ceiling for a nearly new one.
Where the curve flattens
Depreciation slows sharply once the price reaches the level where running costs dominate, because the value is then supported by the car's usefulness rather than its image.
Models with limited production, a distinctive engine or genuine collector interest depart from the pattern entirely and can stabilise or recover.
For the rest, the steepest part of the curve is concentrated in the earliest years, which is precisely the period the first owner pays for.