GHA in general just isn't designed to be secure. Instead of providing solid CI/CD primitives they have normalized letting CI run arbitrary unvetted 3rd-party code - and by nature of it being CD giving it privileged access keys.

It is genuinely a wonder that we haven't seen massive supply-chain compromises yet. Imagine what kind of horror you could do by compromising "actions/cache" and using CD credentials to pivot to everyone's AWS / GCP / Azure environments!