Your list has 14 shootings in the last decade - and includes the attack on Rep. Giffords, a political assassination attempt. Let it be so. Let's also not try and dig for "lower profile" cases in Finland and Norway. We still get 0.04 mass shooting per million in US vs 0.4 in Finland. Are Finns ten times as murderous as Americans? Ridiculous.
Also, look at the map, above the list: if we want to compare apples to apples, Finland is probably comparable not with America as a whole - demographically, economically and socially - but rather with states like New Hampshire, Vermont, Minnesota...which did not have any mass shootings - not a single one in three decades. What does THAT tell you? Eh, approximately nothing.