The trauma he suffered from his past life doesn't just go away. Even if he wants to believe that things are different now, the other worry is that if he lost his status as the Water Spirit King, he would be cast away and hated by the others.
I like that it doesn’t have a speech that solves all of El’s problems, he still has insecurities despite all of the good things going for him. The fact that he is still suffering trauma is very realistic because even though we see it as a long time it hasn’t even been a whole year since he became a spirit king.