FWIW, the reason all of the vertical elements in the C-64 font are two pixels wide is to compensate for raster blur on televisions that were common at the time.

If you made a vertical line only one pixel wide, on many televisions like the Panasonic I used it would be nearly impossible to see.

And while color monitors of the day were an improvement, they still weren't what we would consider acceptable today. I eventually upgraded to a Commodore CM-141, and single pixel vertical lines still weren't great.