I've been watching The Simpsons in Spanish to improve my vocabulary and listening comprehension. I just saw a scene where the use of the subjunctive confused me.
For context, Bart is returning home after running away because he was blamed for ruining Thanksgiving. Before he walks through the door he imagines how his family will react. At first they are happy but then they demand that he apologizes to Lisa and they also all start blaming him for their imperfections.
Homer says: "Tú tienes la culpa de que yo sea calvo."
Grandpa Simpson says: "Tú tienes la culpa de que yo sea viejo."
Maggie: "Tú tienes la culpa de que no pueda hablar."
and Uncle Sam uses "esté" similarly.
I don't understand why they all use the subjunctive. They're blaming him with certainty and they believe what they're saying to be true, so why the subjunctive? Thanks for reading.