The U.S. Supreme Court rejected a petition from Florida casinos Monday, ending a years-long attempt to undo a sports-betting pact between the Seminole Tribe of Florida and Gov. Ron DeSantis (R).

Casino operators asked the high court to block the Interior Department from approving the 2021 deal, which gives the tribe a monopoly over sports-betting in the state—a 30-year deal DeSantis estimated could generate $6 billion for Florida by 2030.

• The decision is the end of the line for the deal’s opponents, who lost a related state constitution-based challenge in the Florida Supreme Court this spring. It appeared the …