Question: Why did Sideshow Bob want to kill Selma? I don't ever recall her doing anything to upset him.
Burns Verkaufen der Kraftwerk - S3-E11
Question: I don't know anything about the stock market, so how could Homer spend $5,200 on beer when he paid only $25?
Chosen answer: Insurance and to get revenge on Bart.
Captain Defenestrator
But how does killing an aunt that Bart doesn't really like get revenge on him?
Even if Bart "doesn't really like" Selma, he doesn't seem to hate her so much that he would be totally careless about her death. If nothing else, he probably realises that his mother would be upset.
He doesn't DISlike Aunt Selma. In any event, he probably doesn't want her to die.
Captain Defenestrator