The company went bankrupt. Bankrupt. They did not have the assets they purported to have.
FTX owed money to a variety of creditors including to crypto traders who deposited. They gambled on handing over their assets to a largely unregulated entity and it went bust.
If a regulated securties broker goes bankrupt you still own the securities. Brokers need to follow very strict laws to be in that position.
FTX faced no such regulation and if you sent them crypto you no longer owned it. FTX did.
And they went bust. What you're saying makes sense if FTX were a US registered securities broker for listed securities on an exchange.
But that wasn't what it was. And they went bust.