“a) food production was simpler then”
irrelevant…things may have been just as treif
And may not have been… I’m going on hearsay, nothing of substance.
Zahavasdad posted earlier that many brands of whiskey are widely considered kosher even without hechsher. That’s because their production is simpler than that of other products, and known to be innocuous. I’ve heard that many more foods were in that category many years ago. I’ve also heard that people were simply ignorant, and assumed things were kosher even though they weren’t necessarily. I suspect that there’s some truth to both of those ideas.
Whether their hora’as heter was somewhat legitimate depends on whether things were really kosher meikar hadin. I don’t have first hand knowledge.