Most restaurant associations are top-heavy with chains and nearly totally controlled by their wishes. The chains all support the bans and he who has the money control the debate.......the mom and pops get steam rolled by them.
It stands to reason that they’d be for “a law” because they couldn’t hold their own in the free market if forced to compete against people who opted to allow smoking in their restaurants.
If you look at most any industry, there’s going to be groups that are willing to prohibit X because if there was a choice of offering only Y, or Y and X, the people who offer the latter are going to do better than those that offer Y alone. If X is smoking, even if the people who offer Y and X were to invest in two separate buildings connected by an airlocked hallway but served by a common kitchen the X alone people are going to insist that their right to do so be restricted because they (at the least) perceive that Y and X proprietors are going to have a leg up on them...