> Isn't the difference here that Federal courts can't create law, only rule on constitutional matters.
Federal courts aren't limited to ruling on Constitutional issues—cases that are purely state law can be in federal court jurisdiction, e.g., because of diversity of citizenship of the parties, and any federal law issue, not just an issue of the Constitution, also qualifies a case for federal court; and they create law just like any other courts (only with broader geographical impact, because it's federal law.)
Federal courts aren't limited to ruling on Constitutional issues—cases that are purely state law can be in federal court jurisdiction, e.g., because of diversity of citizenship of the parties, and any federal law issue, not just an issue of the Constitution, also qualifies a case for federal court; and they create law just like any other courts (only with broader geographical impact, because it's federal law.)