One reaason for this would be what woud happen if they weren't. Imagine this leader in a military conflict. They need to make a speech to rally their country and boost morale. Good luck if you're a shy leader (they'll need it), however an outgoing leader would be enthusiastic and loud.
It is a valued characteristic that any great leader must have. Shyness would not work very well at being a leader. A leader has a lot of people he or she must speak to and they will be asked for advice and they will be great teachers and they have a standard that they have set and must show others how it is done.
Leaders are better when they are people persons. Most people like when people can strike up a conversation and do not make them feel all uncomfortable. They do not have to be to outgoing, though. That also annoys people, when a person can't give an individual a certain amount of attention.
A good leader does not always need to be outgoing. There are circumstances where a leader would lead by example and others would follow through. I think there are some situations that need an outgoing leader but not all. An example of a non outgoing leader would be on a team.
A good leader is able to influence people to do things that they otherwise would not do. This does not require an outgoing personality. In actuality, a great leader will inspire through example. Meaning, a great leader will act the way that they intend their followers to act. This may be specifically a more reserved personality. The Buddha was reserved in this way.
I do not think a good leader needs to be outgoing. I think a good leader just needs to be able to lead and guide people in the best direction. I think that being outgoing is something that isn't necessarily only reserved for good leaders. It is more of a person's social character.
Rose quartz from steven universe was very reserved when she was actually leading and yeah i think this is why it is super necessary to poibt out sobb rg frvfr fgvffgvfr frfrrr grgrgrgr gggg ggggg ggggg gggg grgrg4r grgrgr ggrgr gtgtgt gtgrgr ggtgt gbbgng bfbb tbgtg fgtg gtgtg gtgg gfrgr