Same way you aren't supposed to dump grass clippings or tree debris in the woods. But I dont think anyone would really complain about one tree thrown in the water to create a bass habitat. The law is there to keep say a landscaper from tossing their debris at the end of the day wherever they felt like.
No, the law is there to stop the degradation of our waterways. The problem with the statement you just made is that is the mindset of the majority of people...you feel that one tree wouldn't be an issue. Chances are so do a good portion of the 1451 members of this site..which now means a good deal more then one tree...probably like 1000 trees, and that is just this site, not counting the huge numbers of anglers in this state that don't come here, which could put us up to 10,000 or 50,000 or 100,000 trees..who knows.
Keep in mind, any time you put something into a body of water it changes that water. Yes, it degrades, but in doing so it creates silt, it changes the PH balance of the water as it decays, it raises the nutrient level etc etc. This is a cycle, because as the water changes various plants begin growing, then we poison the waters to control the new growth and so on and so on. Then every one complains that the waters are polluted and laughs how you can't eat fish anymore...None of which is a good scenario and in my opinion people need to start learning how to live with nature, not control it.
I know people love to fish, but leave nature to it's own devices please. There is plenty of natural structure in all bodies to support whatever fish are there.