Japan is ... complicated. NTT is required to offer access to its fiber, but also offers its own Internet service. The Japanese government also continues to be the majority shareholder in NTT, so NTT gets preferential treatment because the Japanese government benefits from NTT’s profitability. The Japanese government also gave direct cash subsidies to NTT for building fiber. Japan also has extremely lax rules for running fiber. If you look around Tokyo, the utilities are hanging out in the open all over the place. That makes the build much cheaper. Also, they’re Japanese so they’re good at building infrastructure.
You couldn’t replicate that in say San Francisco just by separating the infrastructure, while still requiring everything to be buried and look pretty, and requiring unprofitable neighborhoods to be served at the ISP’s expense, etc., and all of the roadblocks places like San Francisco throw up to development. All with San Francisco municipal government types overseeing everything and San Francisco NIMBYs protesting and filing lawsuits over the color of the fiber distribution hubs. It wouldn’t work.