It’s not going to stop. I actually think they will grow in frequency. Keep in mind that while politicians brag about “defeating” ISIS, they are forgetting what the roots of the organization are. Although they hold no more large cities, their motives and determination are still just as strong. They will likely focus on terrorist attacks much more now, until their numbers rise again. They are far from toothless.
These mass killings should worsen, in effectiveness. Some are learning from previous killers, and making adjustments. The Vegas shooter, took a fairly unique strategy, as far as firing from elevation and distance. It was quite effective. First responders simply aren’t equipped to handle such a situation. SWAT is useful, but it takes precious time to mobilize and transport them to a scene. As the time ticks, people are being injured/killed. We’re lucky the Vegas shooter decided to kill himself. He could have hurt more people.
Sadly, it’s pretty easy to kill lots of people, in a surprise attack. Weapons are everywhere, and lots of tactics don’t even involve a gun, or explosives. And then there’s 7 billion people. Lots of potential killers, and plenty potential victims…
Religion was mentioned above. That’s a huge factor, and it isn’t going anywhere.