[Grammar] Why do that? and Why like that?

Teachers,
I know that the following sentences are grammatically correct:
(1) Why do you do that? and
(2) Why is it like that?

But how about the following sentences?
(1) Why do that? and
(2)Why like that?

Are they grammatically correct?
I guess they are not... They don't sound grammatical to me.
What could be the possible reason/s?

I am not a teacher.

It would have been simpler to number your sentences 1,2,3 and 4 rather than 1,2,1 and 2.

Nevertheless, the last two are possible, although they don't mean the same as the first two.

They could have the following meanings:

Why do that? = Why would/should I/you/anyone do that?
Why like that? = Why + verb of your choice + in that way?

Would this mean that the following sentences are complete sentences?
(1) Why do that? and
(2)Why like that?

Are they elliptical sentences?

mamen said:

(2)Why like that?

Click to expand...

***** NOT A TEACHER *****

Mona: How do you pronounce the word "dour"?

Raul then pronounces "dour" one way.

Mona: Why [did you pronounce it] like that? Why [did you] not [pronounce it] like this? (Mona then pronounces it in another way.)


NOTE: In the United States, there are two acceptable ways to pronounce "dour." (It means something like "serious/unfriendly/silent." -- Merriam-Webster Learner's Dictionary (online).

Can we use (1) "Why do that?" and
(2) "Why like that?" in both formal and informal writing?

No. They are both informal.