If your in-dash infotainment system quits working the car is still good for a few things, like driving.
When that ECU and related hardware goes out in, say, 20 or 30 years (let's be REAL optimistic) you're just gonna be SOL. Especially on cars where the ECU controls the A/C, brakes, transmission, etc. On a BMW there isn't much that ISN'T controlled by the ECU or its wicked stepsisters. My brother has an e39 M5 that has spent a total of MONTHS at the dealer for issues with the electronics. Some of them couldn't be diagnosed, much less fixed, even by the factory reps (their responses boiled down to "don't that beat all!") . He has tried every avenue available. It just hit the wall with regard to complexity.
My 69 Camaro will be low-techishly burbling along (reactive electronics in the engine: 1 capacitor and 1 coil.) People will still be driving them in 2069. At least a few. How many 2012 BMW's will still be drivable in 2069? My guess is zero. Even if you put it in storage, some of the solid state stuff will degrade over time, some ESPECIALLY if they're left unused. Chances of finding replacement electronic assemblies or components? Also zero.
Try repairing an analog synthesizer made just 15 years ago. In most cases it's difficult to impossible to obtain the parts. And I can only imagine how much more custom silicon is in a German made ECU.