Not OP but I think it's because it's just difficult to spot it. It's also possible that the clarity of this kind of ice shows the often-black (asphalt) road surface through it without any obvious sign that there's ice there. Could also be a connection to black/evil/cursed.
Probably a bit of all three, depending on who you ask and how they think about it.
I liked unity when they were trying to do interesting changes. I especially liked the attempt at making apps work with the menu at the top of the screen instead of the top of the window (Mac OS style).
When they gave up on that, it became pointless with nothing useful to add.
Not OP but I think it's because it's just difficult to spot it. It's also possible that the clarity of this kind of ice shows the often-black (asphalt) road surface through it without any obvious sign that there's ice there. Could also be a connection to black/evil/cursed.
Probably a bit of all three, depending on who you ask and how they think about it.