A CEX is like leaving your money with the village bar owner:

—Don't worry, kid, it's safe here...

And a month later, he's off to Caños de Meca with everyone's money...

On the other hand, a DEX is like hiding your savings in a can under the olive tree: no one touches it, but if you forget where you buried it… you're in trouble.

The ideal is to use both: in the CEX you buy like in Paqui's store, and in the DEX you store it like our grandparents used to.