Reasoning behind no Nozomi on the JR pass?

Tl;dr: nobody has a clue.

Honestly, I don't know what is going to happen with the Chuo shinkansen, but I'm always impressed with how fast Japan gets train lines up. I was in Japan in Fall '09 and I could see the future Tohoku line being built between Hachinohoe to Shichinohe-Towada. (I was on the old limited express from Aomori to Morioka.) The Nagano line ended in Nagano and there was just one JR East Pass which included the entire Nagano line, the Niigata line, Akita Line, Tohoku line, and Yamagata line. Nothing much had changed in July 2010 when I visited and then I took a 6 year hiatus from visiting Japan because I had a child. When I went back in June 2016, there was a Hokuriku line and trains all the way to Shin-Hakodate. How things go on the upcoming lines depends on how long it takes to purchase land rights and how high a priority the Japanese make building it.

The Hokuriku shinkansen should be extended to Tsuruga by 2022 though so I expect questions surrounding that will come up sooner. I'm really hoping JR Passes can continue to be used on the Kagayaki and Hakutakas because they're really nice. Heck, so are the Hayabusa/Komachis.

Japan has amazing public transport in general and their trains are great. The JR Pass if used correctly is a huge bargain even if it never includes Nozomi and Mizuho.

If a reform of the Japan Rail Pass does no already happen earlier, the opening of the Chuo Shinkansen may be the occasion needed to justify the reform. I could imagine different versions of the pass, one that covers the Chuo Shinkansen, and one that doesn't. I am convinced, though, that if the Japan Rail Pass survived in its current form, it would not cover the Chuo Shinkansen.

Considering the Chou Shinkansen line to Nagoya won't open until 2027 and to Shin-Osaka until 2045, I'm not sure even the Japanese government could say what will happen regarding the JRP.