Because one NASA Administrator in the 90's f---'ing hated the worm with a passion. That's seriously all there is to it.
I worked at NASA about 10 years ago, before the worm revival. The logo was still visible on older equipment from that era, and everyone had a great deal of respect for its design elegance. But Dan Goldin made Worm vs. Meatball a political fight that people still had PTSD from. It took a crafty political outsider like Jim Bridenstein to find a solution that everyone could be happy with.
I think it also helps that after the Shuttle was retired with no successor, people now look back at the worm days (which were the glory days of the Shuttle) with nostalgia.
I worked at NASA about 10 years ago, before the worm revival. The logo was still visible on older equipment from that era, and everyone had a great deal of respect for its design elegance. But Dan Goldin made Worm vs. Meatball a political fight that people still had PTSD from. It took a crafty political outsider like Jim Bridenstein to find a solution that everyone could be happy with.
I think it also helps that after the Shuttle was retired with no successor, people now look back at the worm days (which were the glory days of the Shuttle) with nostalgia.