i think as Lord Voldermort was at his most powerful, with so many wizards were under the imperius curse and noone knew whose side people were on. So there was bound to be alot of paranoia going around.Nobody knew who to trust so they kept important information to themselves.Unluckily, sirius made Pettigrew the potters secret keeper at the last minute. If he'd have stayed secret keeper maybe the potters wouldbe still alive.