Thorough, thought, cough, furlough... Why so many ways of pronouncing OUGH in English?

From a channel Lumen includes in full: RobWords (Rob Watts) explains etymology, spelling, names and the history of English in carefully researched videos, often with linguists as guests and sources cited on screen.

A 6-minute video from RobWords's catalogue; the title names its topic.

Video by RobWords, played through YouTube's embedded player.