Google doesn't need to add its service to every city. If you nail the top ~50 cities, then the rest must compete regardless. It adds massive pressure at a national level when you're talking about tens of millions of people having access to 1gbps, it becomes a cultural talking point, average people start applying pressure to politicians over it.

If you put a 1gbps service in Cincinnati, that forces Cleveland to have to compete with the economic gravity that generates. And they will either respond through attempting to build their own muni broadband or enticing eg Google fiber, or they will suffer and Cincinnati will draw people, capital and talent away from Cleveland.