Why didn't quotas work before the full moratorium?

Quotas that are not enforced credibly against every participant just redirect fishing pressure toward whichever nation is hardest to monitor, leaving total worldwide catch roughly unchanged even as official limits appear to tighten on paper.

Is commercial whaling completely banned today?

No. The 1986 moratorium remains the global default, but a small number of countries continue limited whaling under formal objections to the moratorium or under separate scientific or indigenous subsistence exceptions.

Could this have been prevented earlier?

In principle, enforceable catch limits set decades earlier, before industrial factory ships scaled up catch rates, could have avoided the worst population declines, but no international body with real enforcement power existed until well after the damage was done.

science · 19th century to 1986

The Whaling Commons Collapse: An Open Ocean With No Owner

No nation owned the whales of the open ocean, so no nation had to answer for hunting them toward extinction. It took a near-total industry collapse before an international body could agree to stop.

Facts drawn from NOAA Fisheries, the International Whaling Commission, and Encyclopaedia Britannica; interpretive framing is labeled as modeled analysis.

American whaling, centered in ports like Nantucket and New Bedford, boomed through the mid-19th century, supplying whale oil for lighting and industrial lubrication from a resource that belonged to no one until it was caught, a textbook open-access commons.

[VERIFIED] Industrial factory ships in the 20th century, especially after World War Two, dramatically increased catch efficiency, and several species, including blue whales, were hunted down to a small fraction of their historic population before any effective international limits existed.

Sources

[VERIFIED] The history of American whaling and its role as an open-access resource NOAA Fisheries, A History of Whaling
[VERIFIED] The founding of the International Whaling Commission in 1946 and the adoption of the 1982 moratorium International Whaling Commission, History and Moratorium on Commercial Whaling
[VERIFIED] The broader history and population effects of industrial whaling International Whaling Commission, Whaling