Because it does. The attack has to involve the CI pipeline rather than the dev environment, there's no token to revoke after (if you evict the attacker you're done, the OIDC credentials expire), it's easier to monitor for externally, you can build things like branch protections in and isolate things like "run tests" from "publish", etc. Trusted Publishing is not itself a solution to all supply chain issues but it is a massive improvement.