They guaranteed above-market returns based off of the same ever-increasing-pool math that screwed up social security. Why do you think they’re essentially nonexistent now?
Pensions are nonexistent now because other compensation packages have become the norm. Actuarial regulation has changed to incorporate lessons learned from pension fund failures. The goal of the regulatory changes is to decrease risk to consumers in contemporary actuarial products.
That’s about as deep as I can go on this topic. I’m not an actuary, by a number of my friends are and actuaries talk about lessons learned from failed pensions like engineers talk about lessons learned from failed software development projects. Evidently, demonstrating knowledge of those failures and the resulting controls is a key element of earning the title of professional actuary.
The main difference between car loans and pensions is the time horizon. It’s much simpler to manage the risk of a 3-5 year loan than a 30+ year retirement that begins 45 years in the future.