Why So Many Mass Shootings?

Why have there been so many mass shootings over the past few years?

I wonder aloud for a response to that question:

1. There are more mentally disturbed people nowadays. If that is true, why are there more? And why weren't mentally disturbed people committing so many mass shootings in the past?
2. Guns are too readily available in this country. But people have had guns in this country for over 200 years. Why is it only now that there are so many shootings? How come there weren't shootings like this 50, 100, 150 years ago?
3. People have more hatred than ever before. If that is so, why is there more hatred nowadays?
4. People respect life and each other less nowadays. Is that true?
5. People want attention and fame, even if they die for it.

What do you think? Why have there been so many mass shootings?

(This site tracks the amount of mass shootings for the year 2015.)