Why do people want to be like other people though?

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I notice that I am usually watching someone talk, the way they use their hands or laugh and then I am doing the same thing. Especially those so eloquent in American and British English. I don't even think about it, it just happens. Yesterday my colleague was talking about a film. She was moving her hands around looking so confident making no grammatical errors and he fast paced speech and I caught myself trying to talk the same way when I was talking back to her and everybody else. I was copying the way she was gesturing. I do this with most people I talk to like my colleague. It is pretty funny when I think about it and try to say I adapt to be accepted or to make people feel comfortable around me.
Why do people like me do things, like that with people like my colleague, when we are talking to them?
I believe the real reason I do this is to fit in with the group. Maybe that is the pure true I keep denying. When I was a kid I used to do what my older cousin did. I would walk like him, wear my shirt like he did even though we're different genders, with the front half tucked into my pants and the back half hanging out. I thought this made me look really cool. It did not feel weird, to me at the time. Now when I think about it, it's so funny.
Sometimes things go deep. You look at someone who's confident and relaxed regardless of the stress they're in and they seem to be handling everything with ease. You want to be like that person. So you start trying to talk like them, wear the kind of clothes as them and even think in the same way as them.
It feels pretty good mostly in the beginning. It feels like you are getting better at things.
After some time has passed it starts to get really tiring. You have to keep remembering how to behave, how you should stand. It starts to look like a job. That is what the process of trying to be like someone else is really like. You have to keep working at it all the time. You'll be drained on a daily basis.
I think about children a lot. Children do not pretend much. They just do what feels right when it is happening. Children laugh loudly, they cry very quickly and easily, they run around without caring who is watching them. At some point we learn to watch people and copy what they do. We do this so we can belong with people. We do this because we are not really sure who we are yet. Children are just being themselves. Doing what they want to do.
I still do it sometimes. But when I notice it, I will stop. Sometimes I don't stop. The same thought comes back to me, why do people like me keep trying to be like other people? This is a thing I know yet I still struggle.
I think about sitting sometimes just being quiet I do not need to do anything for anyone. That feels really good. But then the day starts again and there are people, around me and the things people do to be like others starts to happen, it starts with small things.
Funny how the mind works am I right?