Why didn't anybody recognize Steve Rogers in the 1970 scene in Avengers: Endgame?

Because as far as a soldier goes, he looks pretty basic, plus you can't make out his eyes with the sunglasses on.

People may have looked at him and thought he looked like Rogers, but probably dismissed it being him since, as far as they know, he's dead.

As far as they all knew, Captain America was dead 30 years before. They would have no reason to think it's him.