The OS, NeXTStep, would be used as the foundation for OS X when Steve returned to Apple and threw out the entire MacOS codebase due to bugs, legacy cruft, and laughable security.
It’s why macOS has the Dock of icons across the edge of the screen to this day.
Visually, the human brain has an easier job of filling in missing vowels than it does consonants. So it actually makes sense to substitute the O instead of the L.
Now listen here, you little shit…