becasue lots of "things" are interstate.
For folks who complain about the EPA, BLM, Interior Department, etc. You need to read a book called: Renewable Resource Policy by David A. Adams.
Surprisingly the book is unbiased and gives the history of many of those agencies and all the laws passed in regards to natural resources.
Just like unions, a lot of government may have possibly once been necessary, or even helpful, but that point has long passed.
I worked for the DOI, NPS to be exact. Yeah, it ain't needed when there is redundancy created by the state park systems. I went to work for my state's park system. Guess which one not only protects resources, but turns them into a profitable enterprise, provides 75% of it's funding from visitor revenue, AND does the job on a fairly low budget? Let me give you a hint, not the feds.
On the contrary, the NPS is very well funded, marginally protected the resources (I should note that the idiot chief ranger at the site I worked for wanted to perform actions that would damage/destroy the resources on site), wasted gross amounts of money, and has a love of dictating the actions of people off the park (the park I worked for seized a man's family homestead because they could, not because the site was historically significant, and later the park tried to prevent a neighbor from doing what he wanted with his private property, in this case moving a trailer on to it for his sick father to live in so they could take care of him)