Microwave technology isn't superior. That's why it's abandoned.
Optical links are much faster. A single, inexpensive fiber optic cable easily delivers a bitrate of 1000 Mb/s, while a bundle of fibers designed for telecommunications can deliver over 10,000,000 Mb/s. For comparison, a modern high-speed microwave link like AirFiber manages a maximum of about 500 Mb/s, subject to a sufficiently noise-free environment and low-loss path. Of course abandoned microwave links are older and much slower.
Installing a fiber optic cable doesn't require licensing any radio spectrum. RF spectrum is a very limited and economically valuable resource, and you either have to pay a ton of money to get exclusive access, or deal with sharing a few limited, congested allocations with a lot of other people. On the other hand, there's a lot of dirt in which we haven't buried cables yet, and it's relatively inexpensive to purchase rights to bury a cable which is then exclusively yours.
Microwave links are subject to interference from other users on the same frequency, natural noise, and so on. Someone might decide to build a tall building in your path and you can't stop them. At some frequencies, fog and atmospheric haze can significantly degrade the path. Optical cables are relatively robust, perhaps being subject only to the occasional ill-placed backhoe.
Microwave has one big advantage over fiber: it's fast and cheap to install. Put a radio on a tower at one end, and a radio on another tower and the other end and you are good to go. Burying a cable over a similar distance is relatively expensive. But given how valuable communications have become in modern times, the higher installation cost of fiber is offset by the advantages listed above for a great many applications.