Why do drivers do 30 in a 40 with a long queue behind?

[Polome]

Today I followed a 30 mph or less driver in a 40 limit with 12 + cars and building in a queue behind…( with a empty road in front ) what’s the best approach and why do they do it’ ? Are they impervious or just arrogant to the snake building up behind them ? Not much to gain but the frustration of held up drivers can led to doggy overtaking … what’s the answer…