why

[What/Why/Who etc.] the blue blazes (old-fashioned, informal)

if you start a question with what/who/why etc. the blazes, you show that you are very surprised or angry about the thing you are asking about. What the blazes are they doing up on the roof?

See also: blaze, blue, who

Why break the habit of a lifetime? (British & Australian, humorous)

something that you say which means that you do not believe that someone will stop doing something bad that they have done all their lives. 'I must stop writing my essays the night before the deadline.' 'Why break the habit of a lifetime?'

See also: break, habit, lifetime

Why keep a dog and bark yourself? (British & Australian)

something that you say which means there is no purpose in doing something yourself when there is someone else who will do it for you. Just leave the glasses on the table - the bar staff will collect them. After all, why keep a dog and bark yourself?

See also: bark, dog, keep

the whys and (the) wherefores

the reasons for something. I know very little about the whys and the wherefores of the situation.

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why not

there is no reason not to. “Do you want Italian food tonight?” “Sure, why not!” If you're so unhappy there, why not leave right now?

the whys and wherefores (of something)

the reasons for something. The movie doesn't spend much time worrying about the whys and wherefores of its stars' behavior.