It's very simple.
They don't spare a moment to consider those around them.
I have a similar problem with horse riders.
Regularly come up behind a pair of riders side by side, on a narrow road. do they get the horses to step onto the grass for a moment? do they pull into a driveway or farm gateway for a moment? do they pull in one behind the other?
Do they buggery. They carry on, slowly walking their horses side by side, while I am stuck behind them for bloody ages. You can't go round fast, you can't go round close, so waiting for the road to be totally clear the other way long enough for you to crawl past takes forever.
And all the time, they are merrily laughing and chatting their way.
Bitches.
And I can't even lean on my bloody horn, in the internationally recognised code for fucking move, you bloody twats excuse me please, are you aware I am here?
And - and - and - when I finally DO get past them, do you know what they do?
DO YOU???
They give me a regal wave and genteel nod of the head.
That pisses me off more than anything.