Because PONs are just fundamentally worse. Why would anyone turn fiber of all things into a shared medium. Just lay fibers from the dwelling up to the central office. It's barely any costlier since the real expense is the digging, not the fiber. And it's basically guaranteed to scale forever by simply replacing the optics on the ends. That kind of infrastructure can also be leased out to other providers on an individual dwelling granularity. With PONs competitors are forced into reselling bandwidth, at best, or the infrastructure can be monopolised fully.