If you take that data and chart it geographically, you'll find that the death rates are clustered geographically. You'll also find that these "clusters" have a high correlation with economic health.
It is also worth noting that simply categorizing restrictions as "easy, moderate, difficult, or prohibited" is not particularly useful, and is potentially misleading. Connecticut and Hawaii both have, for example, a "difficult" rating for concealed-carry permits. Presumably, they both gained the rating for legally being "may issue" states (meaning that provision exists for the state to issue a permit, but the state is not required to do so), but the laws are very, very different. Hawaii is effectively a "never-issue" state (virtually all permit requests are rejected without consideration - this is a popular method of "we want a ban, but we don't have support for it, so we'll pretend it isn't a ban"). Connecticut is "shall-issue" in practice, because the law (as interpreted by state courts) only allows a permit to be denied if the issuing officer has personal knowledge that won't show up on a background check, and must justify in writing their reasoning for rejection. In practice, the requirements are not much more onerous than those in Ohio (ranked as "easy" in the chart), although it does take longer.