It's been said that Cavafy is "flat" or "prosaic." It certainly can sound like that in translation. Certainly it has a conversational tone (not the same thing as prosaic!).
Does this mean that it is in the demotic register? Yet I have read that he also mixes in touches of more literary Greek, so his language is really more hybrid (not one-dimensional).
People seem very incurious about its prosody. I know that some of it has rhyme and meter. That just disappears in the "flat" English translation.
And the syntax is different in Greek and in English, too.
Colloquial poetry is not just colloquial: the poetic effect emerges from the use of the colloquial as a poetic device in its own right. It is poetic because it violates expectations. (That is one way of looking at it.) The fifth person to write in a colloquial style after it has been done for a while is no longer original.