The difference is obvious when paired together next to each other like that, but the issue with code is often you are looking at examples (often with weary eyes) that are "miles apart" or the only one in a file and trying to spot the difference.

The ligatures that stack a third bar vertically across the space of three characters do jump out at you as much more meaningfully distinct in isolation. You don't have to just count width or whitespace, you have a third "clue" to work with, and sometimes that extra "clue" is incredibly important when you are tired and staring a bunch of code you expected to work and has a subtle bug and need to visually spot the subtle bug.