No matter how many times I read this, it just blows my mind. I can't believe how many people buy new cars--and then dump them right after the steepest part of the depreciation curve. I mean: Thank you, people, for making horrible financial decisions and eating all the depreciation, and then providing a nearly-new car to the market at a steep discount!
It's just that unfortunately the financial system is geared toward making this the "best" option. I don't know about Germany specifically but here for instance if you run a company you can't buy a car and expense it(or get a loan and expense payments for the loan), but a lease is technically a rental so you can expense it, which means that "renting" a brand new car for 3 years is actually cheaper for your company than buying it and keeping it for longer. So yes, you have loads of companies essentially paying for that worst depreciation period in a vehicle's lifetime and then immediately these cars hit the market again.
This results in a fantastic pool of 3-4 year old cars with low odometers and scrupulous maintenance records, keeping the rest of the used market in check.
Due to the slow downs and supply chain issues of the past few years, I imagine the used market is not going to be as nice the next few years, and the usual off-lease classes will be a lot smaller than usual.