A version of what you suggest has been the law since ERISA was passed in 1974.
The problem is what to do if investment performance doesn’t meet expectations, lifespan increases, or future assumed yield decreases. Generally companies had to pay enough to be back to even within seven years. Newspapers sought the right to have thirty years to fully fund. McClatchy was larger than Congress was comfortable with and found itself unable to pay the required fraction of the difference between the NPV and finding amount. Hence, it declared bankruptcy.
There's huge conflicts of interest with defined benefit pensions. It wasn't until PPA of 2006 that standards really tightened up. But imagine being an employer in 1970s. Instead of paying people higher wages, you could create a pension plan on paper, pay the plan however much you wanted (there was wide discretion on what assumptions could be used to calculate the cost of benefits), and get the recipients of the benefits to work for you today for an unknown benefit tomorrow.
If you're one of the decision makers, you're likely to be on the older side. So you're likely to start receiving the benefits soon anyway, and so any underfunding wouldn't affect you, since there would be a couple decades of money available before it started to run out. So the decision makers can easily choose to shortchange those 20 to 40+ years in the future in exchange for enriching themselves in the now (1970s, 80s, etc).
Seems like society should've seen it coming. Of course, if everyone kept having 4 kids, maybe those fantasy numbers could have been met, but who has the ability to predict numbers decades in the future?
The problem is what to do if investment performance doesn’t meet expectations, lifespan increases, or future assumed yield decreases. Generally companies had to pay enough to be back to even within seven years. Newspapers sought the right to have thirty years to fully fund. McClatchy was larger than Congress was comfortable with and found itself unable to pay the required fraction of the difference between the NPV and finding amount. Hence, it declared bankruptcy.