Therefore, just as sin came into the world through one man, and death through sin, and so death spread to all men because all sinned— for sin indeed was in the world before the law was given, but sin is not counted where there is no law. Yet death reigned from Adam to Moses, even over those whose sinning was not like the transgression of Adam, who was a type of the one who was to come.

Adam sinned by seizing forbidden fruit in the middle of the sancturary, in a special, land, in the world (Genesis 2-3).

Once he was cast out there was no way to commit that sin.  It was impossible.  Perhaps attacking the cherubim might count, but we have no such record.

But on Sinai God gave the Law which refers not only to the decalogue but to the Tabernacle that housed the decalogue.  The Tabernacle was placed in a special land in the world.

So now Israel could trespass like Adam had.

The sin “not counted where there is no law” is a relative statement–the equivalent of sinning not like the transgression of Adam.  The sin of the Gentiles were not as serious as the sins that were, as it were, in God’s face.