Question

Why do you think he made it?​

Answer 1

No, it’s not.

In Modern English, the verbs for questions can be:

some form of “to be”: “When were you at the restaurant?”
some verb with an auxiliary
some progressive tense: “Why are you boiling the cabbage?”
some perfect tense: “Why have you done that?”
some flavor of “to do” with a verb: “Do you go out on Fridays?” “Where do you go here to get the best tacos?”
So at the very least it should start “Why do you think…”

What should follow depends on what you’re trying to say. If whoever “he” is arrived in the past, it would be “…he came” or possibly “…he did come”. In the context of having ruled out various possible reasons for his arrival, you might say “Well, then, why do you think he did come?”