Coin security in the block

I am 1 week into crypto. I think Inunderstand that Blockchain keeps good to excellent security of data. Why can’t the “coins” Have the same degree of security? Why can’t there be a stamp on the ADA coins that I purchase to keep them secure forever in the block, whatever exchange or wallet I choose to use. So that if I forget a password, or the exchange I have my ADA is on closed shop or my government shuts it down…my ADA is in the Cardano chain forever?