Before there were smoking band of any kind, so restaurants offered non-smoking sections as a courtesy to the customers who don't want to take their life in their hands just going out for a salad and plate of pasta.
And then once it was the normal requirement to have non-smoking sections, so restaurants went 100% non-smoking because second hand smoke still killed a lot of people, including restaurant employees.
And then eventually the support was overwhelming, so now there is no smoking at all in most jurisdictions.
Why anybody would want to have anybody but a cop packing a gun at the table next to them is a complete mystery. I will simply not go to a restaurant that promotes that. I believe the market will speak regarding open carry.
That still leaves us with a lot of concealed carriers. Eventually these people are going to shoot up enough restaurants that those will be banned. And if a restaurant offers 100% gun free dining (with the exception of uniformed police officers), I will give them all of my business.