Simply because nobody has successfully pitched the Unicode group to add one.

Anyone can pitch new emoji, they just have to go through the fairly easy but strict formal process.

Alex Schmidt, a humor writer (formerly of Cracked and others) did this process for the bison emoji. I enjoyed his “miniseries” about it: https://www.bisonemojipodcast.com/

does the reverse notebooklm exist yet that turns podcasts into longform journalism?

Not that I know of. And I generally prefer written pieces to podcasts :).

The show notes for episode 2 have good references (no fun commentary though): https://www.bisonemojipodcast.com/show-notes