It shouldn't be for "just" any state of the software. We should be able to verify SBOM and take actions at any point. At build time, it is only useful for the developer, I don't get why SBOM is relevant at all. I think you mean at deployment time (when someone installs it - they check SBOM). What I'm saying is, when you fetch the software (download, package manager, appstore,curl|sh), when you "install" it, when you run it, and when it is dormant and unused. At all of those times, SBOM should be checkable. Hashes are useless unless you want people to collect hashes for every executable constantly, including things like software updates.
The problem is, people are looking at it only from their own perspective. People interested in audits and compliance don't care about runtime policy enforcement. People worried about software supplychain compromises, care more about immediate auditability of their environment and ability to take actions.
The recent Shai-Hulud node worm is a good example. Even the best sources were telling people to check specific files at specific locations. There was just one post I found on github issues where someone was suggesting checking the node package cache. Ideally, we would be able to allow-list even js files based on real-time SBOM driven policies. We should be able to easily say "if the software version is published by $developer between dates $start and $end it is disallowed".