Build numbers is engineering, semver is marketing.

Private processes vs what you tell the world.

Build numbers unlocks delta debugging achievement. Add 'last known good' and 'found' build numbers to tickets, along with repo steps, then use diff to find bug.

Build numbers also unlocks QA/testing achievement. Add 'found', 'fixed', 'verified' fields to tickets. Now your team is certain when individual changes are ready to merge, ship/deploy.