If we wanna be frank: lotta tech is in silicon valley and Vegas is probably the closest "large" hub to travel to (Maybe Los Angeles is closer, but not by much). It's the cheapest option without simply staying in SV.
I'm sure the other places suggested would have been nice, but you turn one flight into 2, maybe even 3, have to search for a venue and accommodation for 100s/1000s persons (even if they self book), etc
Conference tourism is big business and the big conferences want friendly places that fit their budget and make it possible for people to attend it
