I have to admit this has been bothering me as well.
So I looked up some info on mass shootings. To say the least, the information is a bit confusing and disjointed. The FBI treats all shootings of 4 or more in a single incident as a mass shooting, regardless of the motivation. This allows incidents like gang related shootings, domestic violence, robberies, among others to be lumped into the statistics.
This seems wrong to me, as I think most of us identify a "mass shooting" as something more along the lines of Columbine or Sandy Hook. To be more specific, a shooting where the body count is the most important concern of the shooter, rather than an unintended consequence.
To this end I looked at only the "deadliest" incidents on record since 1984 and broke them into 8 year periods. No distinction is made between school, workplace or public place, although virtually all were "gun free" zones. I'm simply listing the raw number of shootings of this type during the 8 year periods between then and now.
1984-1992 = 7
1993-2000 = 8
2001-2008 = 9
2009-2015 = 19
You'll notice that the "Obama" years have been the deadliest period to date, with the number of shootings of this type more than doubling in less than an 8 year period. Further, the period of time when the "assault weapons" ban was in effect yielded a net effect of zero on mass shootings.
Does this mean or prove there is a conspiracy afoot? No. But I'm not a big believer in coincidence either. You'll have to draw your own conclusions.