The biggest issue you run into with ISM band mesh networks is they are competing with the rest of the world's WiFi networks. In the 2.4GHz band there's three no

The biggest issue you run into with ISM band mesh networks is they are competing with the rest of the world's WiFi networks. In the 2.4GHz band there's three non-overlapping channels available. If you've got three overlapping networks in some area and they're all using a different overlapping channel you're fine. As soon as the density increases beyond that best case you have channel overlap and interference between the networks. The more users on any individual network the more interference and less usable bandwidth for each node. Enterprise type deployments use tons and tons of micro cells. Each WAP has a low power output so they each end up with a small coverage area and are wired up for backhaul into the core network. Solving mesh routing is pretty straightforward but the physics of the PHY layer are much more difficult. A mesh network in a suburban or rural area ends up more practical than an urban one. Moving to 5GHz for a mesh can help but the range and penetration is much worse. Every node in the mesh would need aerial directional antennas to effectively link to one another. That ends up making everything more expensive or against HOA rules or whatever. Even if you've got all the physical issues handled you've still got bandwidth issues. More than a handful of clients on a node will start to contest for bandwidth. If any connection between sets of nodes bottlenecks through a single node (which happens all the time due to geography) a whole segment of the mesh can have their bandwidth reduced. Meshes are cool and there's lots of capability available at small scales but they tend to fall down quickly at larger scales because they're trying to squeeze into relatively narrow unlicensed radio bands.