People are using "logic" for something that defies "logic".
Young voters determine who is going to win via social media. They're not thinking about a 12 year old performing in Vegas.
Hence, the winner!!!
If AGT wanted to exercise control, they wouldn't let the public vote. They would also lose a lot of the younger viewers. Kind of a two edge sword.
Hopefully, the real talented people will find gigs in showbiz.
__________________
"It doesn't cost "nuttin", to be nice". 
MOM
I just want to do the right thing! Uncle Joe, (my hero).