Except the USA didn't have 100% of world's launch marketshare in 1980's
The Ariane 1 began carrying payloads in 1981. From that moment, we didn't have 100% of the market share even if you only limit it to commercial launches.
More to the point, in the 1980s the Soviet Union and China were launching their own satellites. The Soviet Union averaged over 60 space launches each year. China had launched its first satellite in 1970 on their CZ-1 booster. India launched its first satellite in 1980. Japan launched its first satellite in 1966 and the UK was even earlier.