I don't know if theres a technical reason but to my knowledge i think its based on the person.

For example no matter how happy i ** i never scream and jump up and down, to me i don't understand people who react that way. Now i know that people honestly react that way but thats just not how i react.

So maybe some people cry when they're happy and others jump up and down and others just giggle a little.

So maybe you can't understand why they do it but they don't know why you react your way either, it's just life, we all take life differently.