In both cases it comes down to being lost in the crowd.

In the 1980s only celebrities worried about having their information in a phone book. That, and maybe people with really unique names. That's because getting the information out of a phone book was tedious. The only entity that presumably had a searchable database (other than maybe the NSA) was the phone company. They weren't necessarily trustworthy, but they had better ways of making money than spending all kinds of computer power on individual people. If you wanted to backwards-search a phone number it was an incredibly labour-intensive process without the database.

These days people are much more careful about certain aspects of their identity, but share other things. The thing that's the same is that picking any one person out of a crowd is still hard.

Any one fish in a school of fish is relatively safe from predators because there's no reason for a predator to target them specifically. Or, like the joke about running away from a bear: you don't need to be faster than the bear, just faster than the other guy. In this case, you don't have to be a completely locked down target, you just have to avoid standing out and being an obvious target.