I want to know the difference of each sentence below

Question

1. What brings you here?
2. What makes you come here?
3. Why did you come here?
4. What was your motivation to come her

Is there any difference of meaning between each sentence?

Answer 1

Sentence 2 is slightly incorrect, grammatically. Sentences 1, 2 and 4 effectively means the same thing, :

Why did you come here ?

You could ask a question in many ways. This is an example of that. You want to know why that person has come here. Now, you could ask this in any of the 3 ways you have suggested, and there are many more ways to ask the same. By replacing 'what' instead of 'why', you got another sentence that effectively means the same. Now I'll replace it with 'how':

How come you're here ?

The expected reply to all these questions would be the reason why he has come here. Even though the question has been framed in more than one way, the answer to all remains the same.

On another note, asking "Why are you here?" may seem too direct and some might consider it to be a little indecent. It all depends on your tone. If you ask someone in an elevated and loud voice, the same sentence could be interpreted as "Why the hell are you here?". So it all depends on your tone. Since this sentence is a little too direct, it shouldn't be used in a formal conversation (Ideally). You could ask:

"What brings you here?"

This seems a bit more polite and it generally is a 'calmer' way to ask the same question.

NOTE: May I suggest an edit for the second sentence :

"Why have you come here?"