The big difference: your cars were most likely driven and cared for responsibly.
Mine, was driven hard for 74K miles over 9 years before it was parked (last registered in 1980, anyway) - most likely with a seized engine. Somewhere along those years and miles, mine saw air time - I know because the front and engine cross members were bent upward, as well as the oil pan and even the oil pump pick-up was dented! I had a chain holding my gas tank in, for Pete sake! I'd wager the majority of these cars suffered through all sorts of abusive driving, thanks to the car chase movies and TV shows of the time and all their fan-boys trying to have their fun as well.
With the air shocks "pumped up," the ride would've been stiffer in addition to having the 'ass-end in the air.' When the suspension needed to flex, and the air shocks wouldn't allow it, so the shock mounts would suffer the consequences - since mine had 3/8" lower shock mounting points on the Lakewood traction bars, the upper shock mounting points (rear shock cross member shown above) took the brunt. The vibrations also most likely spun the bolts loose, allowing them to bounce around in there to wallow out the upper mounting points. If that wasn't bad enough, the previous owners torch-cut (real precision work) some adapter plates to sandwich the wallowed-out upper mounting points so the air shocks had 'something' to mount to. The rear shock cross member is literally 1-2mm thick stamped sheet metal... and quite flimsy, all things considered. :shootself:
Not sure what you meant by your last comment. You've been fortunate to have had good luck with air shocks... but it doesn't really measure up when compared to all the countless stories of people having bad experiences with them - I know you're only one success story out of at least 30 people I've heard who've had issues with them.