Ie the books need to balance today, even though they're always going to balance in 30 years.
You seem to be suggesting that they took an unnecessary risk.
Is this my misunderstanding or yours or is it a combination?
The problem is that as rates fall, the shortfall increases. That's still just an accounting artefact, but it looks bad. To mitigate the bad look, the funds entered real hedges, which are now (with rates moving the opposite way) blowing up.
So, my understanding is that the funds took a real and unnecessary risk to mitigate what was basically just "bad optics".
The hedge is because they moved to stocks because of low yields on bonds.