While of course you are technically correct, think about it from the grandma perspective. Grandma uses $app that requires wine, but grandson set her up on Debian stable. She can't run the latest wine because it isn't stable, and it's needed for $app, without updating the system to unstable.

I could be erroneously attributing the intended use case, but I believe this isn't designed for people who know what they're doing; it's for people who don't know, like grandma.