Ahab already pointed out why:
It’s probably easier that way. As the name suggests, they are only similar, but not the same.
Imagine drawing transparent cubes. You take the polygon tool set with a large brush, make the outside lines and press on a key. The shape closes itself.
Then you take the polyline tool, set on a smaller brush, draw the inside lines, press on a key. The line stops.
Instead of clicking the options, changing sizes, possibly enabling or disabling the color fill, you just change brushes with one key press. It’s easier even if you don’t work with only a visible canvas.