If everyone kept their own wallets, bitcoins value would tank to pre-2017 numbers.
The point is, I never need to buy fiat (what you call withdrawing)
And where are you that most counterparties accept BTC? El Salvador?
Normally I would have sympathy but if you post on HN then I have trouble taking it seriously that you can’t figure this out. How could it possibly be any more obvious?
I'm sorry but you lost me here. If I stall my BTC's in a wallet on an exchange, they remain BTC's?
Also I have a feeling that you're not getting my point. It is the selling/buying of BTC's for USD at the BTC exchanges that determines the official BTC/USD rate. Sure you can also exchange them for something else (if the exchange lets you), but this will not affect the BTC/USD rate.
So if on an your exchange you're unable to withdraw your BTC's, you can't sell them, which means you're unable to affect the BTC/USD rate: I.E. BTC price will not go down.
There is a huge subset of bitcoin TrueBelievers™ who regularly buy bitcoin with their local fiat with no intent of ever selling it back for fiat, but instead wait and invest elsewhere in expanding the network of people and institutions who will accept it directly for goods and services, e.g. El Salvador.
Most of these people are ready for a very long winter and a longer game on the order of decades.