Having a standard DIN/double DIN slot for a head unit also makes upgrades/changes easier. With all the new cars having such bespoke and integrated systems, it makes stuff like changing out the head unit much harder.
ex putting a new carplay double DIN head unit is much easier in older cars, and difficult/impossible in newer cars
New-enough passenger cars tend to have connectivity like Carplay as a built-in.
Old-enough passenger cars tend to have a standard-enough hole DIN-ish hole to fit a modern aftermarket unit with modern connectivity.
In between those two, there's a world of cars that have touch-screen controls but lack modern connectivity. This is a subset of vehicles that cannot do anything but shrink as they age out.
But there are some aftermarket solutions for these, too, which add modern connectivity while retaining the stock electronics and physical appearance. (There's actually quite a diverse array of these upgrades available, though the origin of these devices feels very strange to me compared to traditional car audio aftermarket, and it is also absolutely exclusively Chinese.)
ex putting a new carplay double DIN head unit is much easier in older cars, and difficult/impossible in newer cars