I slept on it and still think it is a great question because you noticed something as a learner that I had never noticed in all of my life as a Japanese speaker.
We **DO** say []{} quite frequently and think nothing of it.
We **DO NOT** , however, really say []{}[]{}, etc.
Just like + + , all of those have the same grammatical structure adjective + + . So, what makes the difference?
It seems to me that Japanese speakers are unconsciously treating the phrase as a compound functioning adjectivally in this case. The simplicity and semantic broadness of the word appear to be making it all possible. In short, is an exception to the normal grammar standards.
There may be grammarians out there who insist on the ungrammaticality of the phrase but the truth is people use it and they will understand it if you use it. It has already won its citizenship.