Cars should last more than 20 years. It's only recently with planned obsolescence that the manufacturers have gotten that number down.

It was not. Cars of that era didn't last, as a matter of fact, they would last much less (and require far more maintenance) than the cars of today.

It is true that certain cars (Trabi comes to mind) could be fixed roadside with a screwdriver and a hammer usually, but >100k kilometers life was still rare - people simply used their cars less and for shorter trips those days.

It was quite common. You are right the cars didn't last long and required more maintenance. But also they were much simpler, with lower tolerance parts, so it was easier for lower-skilled mechanics to repair them. Many people around me did that. Another thing is most people used cars much less as you correctly write, so the lower endurance and reliability mattered less.

This is not a sentimental view of good old times, the cars were really bad, killed many people etc, but the fact is because people didn't have a choice they hanged on to them as long as they could. Once modern cars became available, everyone ditched the old ones as fast as they could afford it.

What is currently happenning with cars is not that they last shorter, but after the first life mostly in western/central Europe they are sold to the east and south where they continue to work for many more years, but out of our sight.