There are cheap P2P MW/NIR solution that can provide high bandwidth but it's still not enough.
But they have downsides, range and more importantly density is limited. there is a limit to how many of them you can deploy before they start interfering with one another even tho they are pretty unidirectional put 4-5 of them between 2 buildings and you can start having problems.
The other part is that they aren't as scalable, the main costs of fiber is laying it but you can lay cables with 50-100 fibers at almost the same cost of laying a single fiber.
Fiber can also be upgraded the same cables that gives us 10, 50, a 100 or even a 1000 gbit per second today gave us 1gig or even a 100mbit just some years ago.
The only thing you need to replace are the transmitters and or repeaters if they are used, again those can be expensive but a lot of metro networking equipment is built to be modular and upgradeable the fibers themselves often to not need to be replaced.
Pretty much every upgrade in fiber optics is built around the common diameter and refractive index fibers no one is going to buy into a new technology if they'll have to rip off all of the fibers and put in new ones.
The US and many parts of the world need better networking, it's about time that cities or at least in the case of the US states from local corporations that would deploy the infrastructure and either contract ISP's to do it or do it themselves and lease the lines to them for future use.