Xiaolin Wu lived in vain.

You should use the Bresenhams Line Algorithm for aliased lines instead of just marking all pixels the underlying line touches because that leads to thickness inconsistencies.

I don't get it.

Is the point that the lines are diagonal, rather than vertical or horizontal?

Is it that a proper tool would have anti-aliased them?

Is it that the rightmost lines have been scaled up so have fatter pixels than the others (anisotropically in one case I think)?

My favorite is the 4th from the right.
That has character!