Like Penicillin, DDT was a slow killer, so naturally biologists used to the hitherto rapid biological killers, promptly ignored both

Put a bunch of scientists in a room and get them to bet on a race between a tortoise and a hare and they'll plunk their money on the rabbit every time.

That is one big reason why 'we almost lost DDT and penicillin' , to paraphrase a famous wartime ad from the Ayer agency : a bactericide or insecticide that was slow but steady has no great appeal to your average alpha male scientist......