This take is hilariously misinformed. Japan's long-distance network was almost entirely public until JNR was privatized in 1987, and its successors the JRs continue to be for all intents and purposes controlled by the government.
Some not-very-light reading about the rise and fall of JNR:
This is entirely wrong. Jees this is so infuriating to see repeated. Japan has ~100 train companies. JR is 1 of those (now 7). The rest are not. Hanshin, Hankyu, Keio, Keikyu, Tokyu, Toei, etc all giant train companies, all private, have been since they were foudned.
No, it's not. The successful private companies all serve suburban commuters. The long-distance network was almost entirely JNR.
As of 1996, JR group still controls over 20,000 km of Japan's 30,000 km of rail, and that's after privatizing and closing a large slab of it (mostly those duplicated by Shinkansen).
The long distance is mostly irrelevant, People use trains daily for short commutes. As for JR, the arguably only reason it was in the position it was in was because the government got in the way. If they'd stayed out of the way the private companies would have built the rest.
Further, JR started private. It was nationalized in 1906. The Tokaido Line and tha Sanyo Line already built by private companies. They forced out 17 other companies and then ran it into the ground.
The only place private "might" not have built is rural and JR built those mostly as "pork-barrel" (favors to politians) when it was run by the government. I also say "might" because it is/was common, not just in Japan, to build housing and trains to that housing. You pick a place like Enoshima, build a few 1000s homes, build a train out there to sell the homes. So "rural" places do get private trains.