Quick analysis:
There has only been this "increase" since 2010, otherwise, the two trend lines tracked with the "permissive states" being slightly higher, most of the time. When mass shootings are already extremely unlikely events, I don't think a "trend" of just 5 years is enough to make such analysis.
Any one mass shooting event can skew the numbers dramatically. We are talking about 344 events in a population of 330M+. That's a rather small sample size.