As a bunch of Ledger owners are finding out, there are reasons for FDIC insurance of banks and that reason is so that people don’t have to be exposed to the dangers of storing all their money under their mattresses

The FDIC is a scam. If JPMorgan or Wells Fargo failed they would not have enough to cover the loss. In fact they only hold ~2% of what they insure which would leave 98% of people with nothing. The only reason the FDIC is not bankrupt is because a cascade of banks have not failed all at once

what happens when a Ledger update bricks it?

The recent incident was a software supply chain attack. I am not aware of a bricked update but thats not saying much since i dont follow them closely

the company decides to backdoor it to escrow your “private” keys?

You lose all trust in them as you should and no longer use their products.

what can you do with those hardwallet funds besides HODL?

That is the point of a hardware wallet to hold your funds securely until you want to use them.

expose all of it to danger to do so?

Your hardware wallet acts as savings and use a hot wallet as a spend account with less money in it.