It has, inflation is rising rapidly in no small part due to the gov printing money to cover its obligations, of which social security is one of the largest and will only become larger as the cost of living increases due to said inflation- a vicious cycle. If contributions don't cover the payouts (which they don't, and never will unless you tax the younger generations to death) then the difference has to be made up with printing, which will of course cause inflation

You are right that they will continue printing money regardless, and at this point it's too late for a 20% reduction to fix anything. Might as well just take the checks while you can and make the most of it, not much else you can do. But that doesn't mean its sustainable or will last forever.