>

Probably because there is a high chance that it is being recorded with a better angle, better quality camera and not interfering people around you.
I hope someone holds a screen up that blocks your view, at every event you go to. >

I hate to break it to you but a phone screen won’t block your view >

Numerous phones, and the hands holding them, can quite easily block the view.  
The last concert I went to, I could see the artists on stage for less than ten percent of the duration of the concert. It's incredibly inconsiderate. >

I think it's a popular opinion to be honest >

not unpopular. having your phone up taking pictures or recording/streaming video THE ENTIRE EVENT or a significant portion of it is not fine. >

Watch it now because even though you are recording it, you'll never watch it again. >

You can do both??? >

Exactly!  We have the technology to rewatch our favorite memories so why not put it to use?