Why was the Netherlands Antilles flag retired in 2010?

The flag of the Netherlands Antilles was retired on October 10, 2010, because the political entity itself was dissolved on that date.1

Following an agreement reached in 2006 between the Dutch government and the remaining five islands, the federation was dismantled to reorganize the status of its constituent parts. Upon the dissolution:2

• Curaçao and Sint Maarten became autonomous countries within the Kingdom of the Netherlands, attaining a status similar to that of Aruba, which had seceded from the federation in 1986.12
• Bonaire, Saba, and Sint Eustatius became special municipalities with closer ties to the central government of the Netherlands.2

Because the Netherlands Antilles ceased to exist as a unified autonomous territory, the flag representing that specific federation was retired.1