"Worthy" being an adjective, it should be syntactically correct to use it as the qualifier in a "subject" + "linking verb" + "adjective" structure.

Thus, it should be syntactically correct to say "...it is worthy" rather than "...it is worth it".

"It is worth it", anyway, seems to be a syntactic abomination.

Where does "worth it" come from? A grammarian said to me many years ago that it is an American "idiom". He however could not explain why "it is worthy" is considered incorrect vis-à-vis "it is worth it".

Would anybody volunteer here with an authoritative answer?