I think the fear people have is an attacker storing captured encrypted data and decrypting it later. It may be five or ten years out of date by the time it is decrypted, but even then it could still prove to be fruitful for the attacker.

I'm sure many oppressive regimes would love to know what their citizens where privately talking about, even if it was ten years ago. I think its a valid concern that quantum computing might take off, and in ten years you could run shores algo on an AWS instance. Long con attackers could MITM chats for juicy blackmail in the future.