why does everybody assume that whoever is Satoshi still has access to their wallet? It's absolutely possible whoever is Satoshi has simply lost the key.

We're talking new technology where you're running fast and loose. It's absolutely possible, and I'd say a big reason why someone would not want to admit to being Satoshi.

I'm Satoshi, but I also lost billions because I messed up a Debian upgrade.

Further, no one would believe them, and they'd still endlessly be a target for criminals. No benefit to revealing any information beyond mild dismissals, IMO.

Or what if Satoshi deliberately destroyed their key?

The motivations behind Bitcoin were clear.

All the wealthy people I know don’t really do it for the money. The money is the gauge or the metric they use to judge how well they are playing the game but what motivates them is the love of the game and their sense of purpose.

If someone was to truly believe that Bitcoin was going to be a gold/USD/Eurodollar/swift etc. replacement then their metric of success isn’t money if they got in early.