Assuming you literally mean "closed-source" (and not just closed weight), then yes I totally agree - it would be really nice if the training data for some LLM were reliably (and ethically sourced), but more important to our assurance of the model that it is byte-for-byte reproducible by us, as to prevent these "sleeper agents" from appearing.

There would not be the same incentive, closed models wouldn’t want to steal from / Trojan agent swarm their paying customers