by Carl » October 25th, 2013, 3:06 am
And how old are you?
Mufasa was old. OLD. He was visibly old and he was a monarch. The more a person ages and takes on more responsibility, the more stressed they get and the less they feel like goofing around and being "cool" and the less time they have for "loosening up." As Mufasa says, being king doesn't mean getting your way all the time. It's not a cakewalk, and neither is being a parent. Having that kind of responsibility is stressful.
As king, Mufasa has to make sure the entire kingdom runs smoothly. He has to sort out any issues between the animal species living in the Pridelands and he has many duties to attend to. There are more things that would require his attention than I can come up with in a moment to jot down. It's a very busy life, being king.
As a parent, he has to take care of his son. He has to impart knowledge onto him and train him to become a king himself. He has to make sure he stays out of trouble and that he is well fed. He has to make sure that Simba has everything he needs, that Sarabi does, that Sarafina and Nala do, and that the whole pride does.
Think of it like this: imagine a human family. The dad runs a company. He has a wife who is a stay at home mom, a son, and a mother and father who are retired. He has bills to pay, he has decisions to make regarding his business, he has issues between employees to work out, issues between customers and employees to deal with, and he has to come up with new ideas to keep the company fresh and in competition. Is this guy going to be "cool" or "loosened up"? No, he's going to be busy, stressed and tired.
It's not exactly the same, but Mufasa's place is kind of like that. Add in that he's always dealing with Scar and it's no wonder that he's not swinging from vines and dancing and having a merry old time with the gang. Why would he? He has much more important things to attend to.
And, actually, adult Simba was only "cool" as you mean it before he had responsibilities. In the sequel, he was even more uptight than Mufasa. Why? Because he wasn't prepared for all of that stress and responsibility and it's harder for him to handle it.
Tl;dr people become less happy-go-lucky and fun when they have to do serious things like run a whole kingdom. It happens to everyone, and it doesn't take anywhere near as much as Mufasa had to deal with to turn most people into a buzzkill.