I sound like a broken record, but I bring this up about every time I hear about this, because I've seen the effects of one losing their pension in the form of very old men and women having to work until they die due to Studebaker's pension going bust.
From here:
en.wikipedia.org
"No insurance for defined contribution plans[edit]
One reason Congress enacted ERISA was "to prevent the 'great personal tragedy' suffered by employees whose vested benefits are not paid when pension plans are terminated."
[26] When a defined benefit plan is properly funded by its sponsor, its assets should be approximately equal to its liability, and any shortfall (including benefit improvements) should be
amortized in a relatively short period of time. Before ERISA, employers and willing unions could agree to increase benefits with little thought to how to pay for them. A classic case of the unfortunate consequences of an underfunded pension plan is the 1963 shutdown of
Studebaker automobile operations in
South Bend, Indiana, in which 4,500 workers lost 85% of their vested benefits.
[26] One of ERISA's stated intentions was to minimize underfunding in defined benefit plans."