How to identify the simple subject of the sentence:
(1) There is a word that functions as an adverb of place. In the sentence, it is used in front position. It refers to the subject.
(2) "Are" is the be verb.
(3) "Too" is an adverb modifying the adjective "many".
(4) "Many" is an adjective modifying the noun.
(5) "People" is the simple subject.
(6) "On this elevator" is a prepositional phrase.
If you want to have the complete subject, it is "too many people."
