I think there are 2 kinds of people who do that.
1 is the type that do it on purpose because they want to be noticed and probably hoping someone will blow their horn or make a comment so they can blow up at them about being a pedestrian or that they should be patient. They want people to be annoyed by them and they want conflict where they feel they are justified.
2 people who don't think about it because they have absolutely no consideration for others, just assume wherever they walk everyone else will get out of their way, have no concept of safety for themselves or others and just basically oblivious to everyone else because all they care about is themselves.
They are pretty much the same assholes that when walking around the road intended for cars will walk in a diagonal line to where they want to go increasing their time spent in the road take 5x as long instead of simply walking straight across then up to where they are going.