You're making the assumption the majority of the people playing pool at a bar or billiards room are hard core dedicated pool players. Keep in mind you're dealing with a business where the fixed cost is relatively high making volume everything. Losing just 5 to 10% of your business can be devastating. Lose 20% of your volume and you're probably out of business.
Given time, a new market may emerge and could even be bigger (attracting non smokers, families, etc.). I'm guessing in many if not most cases, these billiards halls will have to do some remodeling in order to attract much of that market share, which requires money. The other key words are "given time". What does the business owner do to survive until these "new Customers" start coming in? The transition certainly won't be instantaneous.
I remember going into an upscale bar in Lexington, KY soon after the smoking ban was enacted there. It was deserted at a time it had always been packed the numerous times I'd previously been there. I was chatting with the bartender who was a non-smoker. I made the comment about how he must be ecstatic about the smoking ban. He laughed and said absolutely not, while he might now avoid cancer from from second hand smoke, he'd likely starve to death (from lack of income) before the cancer symptoms would even begin.
They established smoking bans in Marion County (Indianapolis) about a month ago. I've noticed a substantial decrease in business at the bar we play APA League at. We played there last week, there is normally a fairly brisk business on Tuesday night because of Karaoke. The only person singing this past Tuesday was the Karaoke Operator, it was practically deserted except for the APA League players.