The clause after an adjective is an adverbial clause of reason, which is called an adjective object clause in some grammar books. Therefore, some teachers may call it an object clause, while others call it an adverbial clause. In fact, according to standard grammar, only prepositions and verbs can take objects. Therefore, this kind of clause can only be defined as adverbial clause of reason to explain the reason of the preceding adjective. Such adjectives often express various human emotions.
I'm sorry you're in a bad mood.
I'm glad you can help me.
I am sorry that he left me alone.
I am very excited because I passed the exam.