I think this report hits the nail squarely on the head.
Here's why:
Back in the 80s and 90s in the UK we had two major sporting disasters.
First The Bradford Stadium fire.
Source
Second The Hillsborough Disaster.
Source
The problem we in the UK had was Football (Soccer) violence. Gangs of opposing fans battling on the terraces, in the streets, pubs, towns. Often the 'fans' arranged the battles before the match.
Since both disasters, where many people lost their lives, all-seating stadiums have been implemented throughout the country.
Before that, 'The Terraces' - parts of the stadium which held spectators in standing-only areas - were battlegrounds too. Sometimes the home and the away fans were parted by the flimsiest fences which did nothing to separate them if they wanted to 'rumble'.
After the safety-measures passed into law, all-seating stadiums mean fewer spectators are packed in to larger spaces and they can't get the leverage to fight, because of the seating.
It's a small thing in comparison to gun laws, but it has made a difference to our sporting events (football/soccer).
I've not done the research into other spectator sporting events - Rugby, Athletics, show-jumping etc - to see if they are all-seating stadiums, but we didn't get any violence in those sports.
In essence, the government wanted a way to combat a problem (violence every Saturday, leading to heavy and costly police presence in the towns) and a solution was found because of a couple of disasters - one of which, the police have been heavily criticised for not only the poor handling of the problem as it started, but even in exacerbating it once it became more than a 'problem' and people started dying.
Good post, thank you.
RE: The expected response from the shooting in Las Vegas