Pensions have been used for decades by companies as incentive to attract employees to work for them in lieu of a higher salary. It isn't about robbing Peter to pay Paul, rather I'll continue to pay you in retirement in exchange for less money today.
Pensions ARE regulated (obviously not enough) in order to qualify for preferential tax treatment and do have some guarantee through Pension Benefit Guarantee Corp (PBGC), a govt organization.
https://www.pbgc.gov/about/new-to-pbgc The problems of today are a result of three issues primarily, two of them are related to corporate greed. First, in an effort to maximize corporate profit, the companies have been using creative actuarial and accounting assumptions related to life expectancy etc. resulting in severe underfunding of the obligation. Second, as companies get bought by other (sometimes smaller and more leveraged) groups, the buying group raids the pension to help fund their purchase. That part is really just theft. Third, the funds that have been set aside to fund the obligation are generally invested in safe, mostly govt backed investments. Treasuries just don't pay near the return that the actuaries have assumed.
So, for those who are cool with less regulation of corporations and maximizing profit. Enjoy the mess because it is largely on your shoulders.