So, in the sentence "I went home because it was getting late." Is the the sentence pattern of "it was getting late" is (Subject - Transitive Verb - Direct Object) or (Subject - Linking Verb - Predicate Adjective)
it was getting late
get is a linking verb, and was getting is its past continuous tense.
late is an adjective functioning as subject complement.
The sentence structure is hence Subject - Linking Verb - Adjective.
get has one of its meanings to become or start to be.
You're getting to be such a big boy, aren't you!