It's because they're two different variables. width in line 2 belongs to the user program, while the other width belongs to the format function (noted by {width}).

Although not exactly the same, a similar example would be a variable defined in a function versus after (and outside of) one:

def func(x):
    return x + x

x = 12
func()

Which returns the following:

Traceback (most recent call last):
  File "<stdin>", line 5, in <module>
TypeError: func() missing 1 required positional argument: 'x'