Traditional city boundaries rally aren't meaningful in discussing market size. Metro area size is better, but not perfect as some cover very large land areas or are hemmed in by adjacent areas.
I think a good argument can be made that only New York and LA are large enough to support multiple teams. The New York metro area is more than twice as large as Chicago. So is LA if you include Riverside-San Bernardino-Ontario. Chicago is a distant third and seems likely to be passed by Dallas and Houston in the next few years. Philadelphia is eighth.
The top 20 (if Riverside is included with LA) all have teams. From 21-30, only three had teams (St. Louis, Pittsburgh, Cincinnati); a fourth will get one going forward (Sacramento followed by Las Vegas). Kansas City is 31st, Cleveland 33, and Milwaukee 40. (Toronto of course is not in the census data.)
You could do a lot more manipulation by considering adjacent/nearby areas within others (e.g., Austin/San Antonio within Houston, Columbus with one of the Ohio cities, Louisville with Cincinnati, etc.) But it doesn't change the case much, except for perhaps that Texas could accommodate a third team.
These numbers are based on Public U.S. Census Bureau figures, which you can view by clicking on one oft the Excel icons on this page: