What is currency if not an implied promise that someone will provide future services or goods in exchange for it? In a situation where workers can't/won't keep a promise to maintain retirees, the currency value will reflect exactly that, it will devalue so that the total amount of currency retirees have won't be enough to buy these services.

Yes, but we'll quickly spiral into infinity if we take it too far. For our intents and purposes, currency is a placeholder for value. If you have that value (whether actually material or represented by currency), you'll have a much better chance to find someone who will exchange it for services. Their incentive is getting something from you in exchange.

On the other hand, in the current system as it's used in France, Germany etc, their incentive is that hopefully someone else will do it for them in 40 years. But from what I gather, very few members of GenZ believe that our pension system will survive in its current form until it's their turn to benefit from it. They expect it to collapse, so everything they'd now put in would be wasted, much like if you invest in something after it has signaled that it will default soon.