It's like with the justice system: if you have to choose between the risk of jailing an innocent and the risk letting a guilty person go free, you choose to let a guilty person go free. All the time.
Unless you're 100% sure that a student cheated, you don't punish them. And you don't ask them to prove they're innocent.
Unless you're 100% sure that a student cheated, you don't punish them. And you don't ask them to prove they're innocent.