My Lion King Forum

Well I think there's two reasons, as many wrote above. The general one of course is that maturing happens when you grow up. It's called life. Although hard to say how Simba's personality would have been if Mufasa was alive, but I assume a bit softer and playful, maybe having some typical teenage issues etc.

And from the story POV, Simba's innocent and happy life changed dramatically when Mufasa died. He didn't have a change to grow up normally, instead got a huge blame on his shoulders such a young age, living in a lie while heartbreaking false guilt ate his innermost which eventually turned out to be a not his fault. Naturally that changes personality. And I don't think Simba can ever get over with his father's murder completely. Yeah, he has managed to move on in his life, rule and have kids but his past in a way, hurts him forever. It can bee seen in his adulthood, how he wants to live up to Mufasa's expectations and is overprotective towards Kiara (fear of losing her like he lost his father) in SP. And in TLG when he and Kion talks to Mufasa, it can be seen how he misses his father and his wisdom.