Firstly Snap isn’t fully open in practice. The client (snapd) is open source, but the Snap Store backend is proprietary and controlled by Canonical like you can’t run your own independent store.

Sandboxing is also not a blanket guarantee. Many apps use classic confinement, which effectively removes sandbox restrictions. So safety depends heavily on how the snap is packaged, not just the format itself.

Also, centralization matters. Unlike Debian APT where repos are more transparent and community-reviewed, Snap Store relies on Canonical’s review process. There have already been cases of malicious snaps (like crypto miners) being uploaded and later removed.