Probably for the same reason that seatbelts had delayed adoption by motor companies. Money. Also, I don't think that they knew how to make cars that had different crumple zones.

For the same reason people are surprised by these videos (I thought they were built like tanks!), presumably people thought "I want to make it safe, I'll build it like a tank".

Maybe there was a general feeling of "if building it like a tank doesn't work, maybe cars just can't be made safe in the event of a crash?"

We are talking a car from 1959 in the original link - before computer modelling, before low tolerance robotic manufacturing and assembly, before fast response electronics for airbags and seatbelt pretensioners, before the data from crash tests could be collected in an automated fashion. We're talking before stereo sound here. The past is a foreign country, we can't judge it by our standards applied to hindsight.

(Apologies if 1959 is within your memory - for me it may as well be the dark ages ;)

Also, cars were meant to carry you from A to B. They shipped because they could do that and make a profit. Survival in the event of an accident is sort of a side benefit.