#English
Sentence : "Why did he go home?"
Once we are in the past using "did" we put rest of the verbs in present. As like : We are talking about the past and therefore once we are living in the past, now lets talk about it as if this is our present.
Which is why "Why did he went home?" is wrong.
Mnemonic to remember it : "Why did he did it?" sounds naturally wrong. Two "did"s. Correct should be "Why did he do it?"