I see the point you're making and it's valid, however, there's one component that's missing. Unlike prior to Fiber, there's now Gigabit offerings from Comcast and AT&T and in many places, Comcast and AT&T are the two available options for internet service. In reality, it's the fact that those two companies are providing Gigabit (and multi-gig service) that's causing the expansion of gigabit service nationwide at this point.

Google Fiber was never offered in my area nor was it even hinted at being a future Fiber city, but Comcast currently offers multi-gig service. I'm not sure about AT&T because my past experience with them has had me swear them off. They could offer next-to-free service and I'd turn it down, so I don't pay attention to their offerings in my area, but I am able to get top-tier U-Verse TV/Internet in my home so I'd imagine gig will be around the corner at some point. Google Fiber wouldn't cause this expansion over here, though it may have been responsible for the initial expansion (or even the idea of delivering speeds like that to consumers). The "cat is out of the bag" so to say. The (limited) competition exists and isn't going to go away with Fiber out of the picture. I think Google saw this and realized it was a somewhat safe time to shed the expense/headaches they're having getting Fiber rolled out nationwide.

And then there's the start-up factor. In the City of Detroit, I'm aware of one small company that's offering (building-to-building) gigabit service on par with Google Fiber. These micro-ISPs probably won't get a footprint the size of Fiber, but if enough of them pop up, the combined numbers might reach that point, further forcing the incumbent's hands. It's not a terrible business to get into the way some of these start-ups are funding their efforts. The fact stands that practically nobody who has worked with the customer service arms of their "big company" ISPs anything positive to say about them. I pay 2.5 times the price of residential broadband for the same speed to get better customer service out of Comcast[0], and I wouldn't dream of leaving Comcast Business for AT&T Business or Comcast or AT&T consumer. I work at home, I need reliable service without caps and nonsense, and I need to know I can get a service call handled quickly when problems arise. If a start-up came to my area offering faster speeds at the same or better price, despite my relative happiness with Comcast, I'd switch just because I know at some point they're going to discover the expense they're paying for Comcast Business's service isn't necessary because "We're a utility company. We don't have to care."

[0] The service paid for itself a while back when I took the bait for U-Verse TV service (offered at a huge discount for 6-months and no cancellation penalty -- yes, I cancelled), and the contractor from AT&T -- who's eyes were bloodshot and speech was slurred -- came to bury my U-Verse wire and managed to cleanly slice my Comcast Business Internet cable. I called at 5:00 PM and they had a guy out at 6:30 PM same day who ran a completely new cable, hooked it all back up, and did so apologising for the service disruption that was their competitor's inept contractor's fault. He was done by 7:00 PM and despite this not being Comcast's fault, I was not charged for the service call (which I would have been fine with paying for). I have not had a single outage lasting more than 15 minutes in three years (which was one time, though, luck may be a factor here), and their Business help line gets me to a proper English speaking representative who doesn't just recite "did you turn it on and then off again" from a script. It's actually a bit distressing knowing that this same company, which deserves its terrible service reputation on the residential side is perfectly capable of providing service bordering on fantastic, but just doesn't (unless you opt into a substantially higher bill).