it isn't raining vs it doesn't rain

Question

Let's go out now. It isn't raining any more (not It doesn't rain)

(This is from Grammar in Use of Cambridge.)

I thought those two are valid form but the book say it is not.

Is the reason just idiomatic or semantic?

Answer 1

Only "it isn't raining" is correct. Since "to rain" is an active verb (not a stative verb), the present progressive is used for action taking place right now, and the simple present is used for habitual action.

It is raining.

Right now, rain is falling from the sky.

It isn't raining.

Right now, rain is not falling from the sky.

It rains (in Rio de Janeiro).

Sometimes there is rain in Rio de Janeiro.

It doesn't rain (in Dubai).

There is never rain in Dubai.

In your sentence, it is clear that we are talking about "right now" and not "habitual action," and so only the progressive works.