Its mostly about sharing it with friends and social media. I dont know why these people feel the need to do this either. The healthiest thing I did last year was quitting all (common) social media platforms like Instagram, reddit and stuff like that. Life is much slower and I dont feel the need to check my phone every few minutes anymore (I barely posted anything anyway).
I guess people are addicted to new notifications. They are lonely and drawn to human interactions and attention through social media because they are incapable of getting it through real life.
I guess people want to prove they were authentically there, experiencing it themselves instead of watching it on TV. And I sort of get it. When I'm on vacation, I like making my own photos of everything, even if professional photographers have already made hundreds of far better photos of it. Somehow the ones I made mean more to me. And I don't even share those photos on social media.
So on the one hand making your own photos and movies at events is less authentic than just experiencing it, and yet at the same time more authentic than relying on professionals to film it for you.