Microwave links (including point-to-point "line-of-sight" links) transmit a cigar-shaped cone of signal which raises the noise floor for all receivers within earshot of a given frequency at a given location. The absolute physical dimensions of the cone of signal are dictated by the specific frequency being transmitted, the size and shape of the antenna, and the distance from the transmitter. This makes interference (including self-interference) one of the bigger challenges to colocating many links in the same geographical area.

One of the promises of millimeter-wave radios (radios which operate at frequencies from 18Ghz-100+Ghz) is that they are less prone to interference because they operate at such high frequencies.

Presumably, one of the bigger reasons to use free space optics is that it results in an almost total elimination of interference. No interference means no coordination is necessary between operators. No coordination between operators means no licensing/regulations are necessary for maximizing use of the available spectrum. Non-regulated or lightly-regulated technologies can have much broader adoption in the marketplace.

Lots of good reasons to pursue something like this.