Well, they were very expensive and most of them were NOT to save the public but instead too perform scientific experiments. Look at vault 11 for example. The people of the vault were told to kill one person every year or everyone would be killed. read more
It would be extremely expensive to build shelters and it wouldn’t be really justifiable as the whole “Soviets are going to nuke us all, build a backyard shelter” craze pretty much ended in the 60s. The U.S. also has a very diversely structured and distributed population. read more