The legal basis for the ruling didn’t hinge on the act of gambling, but rather on the 10th Amendment, which defines the relationship between the federal and state governments. The court said the 1992 ban violated the “commandeering clause” of the amendment, which says that while Congress can pre-empt the states from taking certain actions, it can’t order the states to take certain actions. In this case, the court said the 1992 law ordered states to take actions to prohibit sports betting. (As an aside, the commandeering clause is why, say, the Trump administration can order federal immigration officers to arrest immigrants who are in the country illegally, but can’t make a state, such as New York, do so.)

https://www.newsday.com/news/region-state/supreme-court-sports-betting-decision-1.18591934