Here are two example sentences that I really need your help to clarify:
Why don't you bother to take a bath?
(Should the receiver take or not take a bath?)
He should, if he cares what the asker thinks.
It means "Why don't you take the trouble to have a bath occasionally; you stink!"
Why did you bother to call her? = Past Tense
(She should call or should not call?)
She has already called. The questioner is asking her why she bothered.
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