alt Hacker News> It runs them on pushes
Sure, because pushes are how you update a reference. That’s really what triggers an action: a reference changing. And there could be a bunch of those in a push.
A commit costs storage, you’ve got secret scanning, it needs to be indexed in a way that can be referenced in commit messages and comments, a commit message itself can close issues or reference other PRs, stored and served individually and immediately via the web UI or git clients, etc etc.
It’s also like… the core unit of git.
None of the things you mention - indexing or secret scan would be done individually for each commit. As I already said, this would be a log of all commits in the range pushed - it would be scanned once for those things. There is no need for a loop running over a range of commits and processing each one.