the justification for not doing that is probably "prohibitively expensive given the amount of data involved". they'd need a bunch of human reviewers combing through massive troves of data. it's probably cheaper to "sort of fix" it after the fact.

> perhaps there's ways to bucket training data such that the model is aware of which data leans factual (quantifiable) and which data leans opinion (fuzzy, qualifiable)

as a lecturer once said to me about my idea for a masters dissertation project that would classify news sites based on right/left tendencies -- "that sounds dangerously political". especially given the current let's all shout at each other political climate.

aside: someone built this and it was a fully fledged company, which has always annoyed me.