The NFL has always supported any type of legislation, whether federal or local, that prohibits sports betting. This is nothing new and goes back many, many decades.
The NFL has the old school view that sports betting taints the game. The NFL is afraid that underworld gamblers will pay off players to throw games. The NFL is also afraid that advertisers, fans etc. will think the games have been rigged in some way as long as there are legal ways to bet on games.
Of course, with the salaries players make these days, such notions are ridiculous. But in the past, when players and coaches did not receive equitable shares in the profits, the possibility of players throwing games for money was a real possibility.