Is there a reason why FiraCode Nerd Font Mono has no Oblique or Italic?

[unphased]

For example this has italic. https://github.com/zwaldowski/Fira/tree/zwaldowski/mod-new/otf

[Finii]

Well, Fira Code (https://github.com/tonsky/FiraCode) does not have slanted glyphs.
Compare

• When will you making italic for this font??????  tonsky/FiraCode#1266

The font you linked is not Fira Code but Fira. That would be the Fira Mono we have in the patched-fonts/. And the font you linked also has no slanted mono variant...:

Of course you can always just take Zwaldowski's Fira Sans font and self-patch the symbols in. But that is not a monospaced font.