Because not is the abbreviation of is not, it is the verb to be, so you can't add the verb prototype after the verb to be, nor can you add one every other word, but you can add the present continuous or past participle;

Not is a common spoken extension of is not. He's flashy, isn't he?

He is dressed in luxury, isn't he?

There is not enough time to get there now.

There is simply not enough time to get there now.

His work is not so good.

His work is not very good.

Life is not like a movie, you know.

You know, life is not like a movie.

Essentially, your situation is no different from mine.

Essentially, you and I are not far apart.

This idea is not new.

This idea is not new.