Why is unfunded pension liabilities to GDP not a regularly monitored metric?

In the UK we have an estimated £5trn in unfunded pension liabilities, including state pension and public sector pensions.

These figures are from 2018, so are likely much higher than this now.

This is 2.5x larger than the national debt (1.8trn in 2018) and also cannot be inflated away like the debt.

Why is this metric not more commonly discussed or tracked? The latest data I could find easily was from 2018.