Where are you downtown that there are bushes? Most people just throw their shit out on the street. While yes there's definitely a behavior problem, I also get peeved at the number of property owners that can't be bothered to go out and pick up the trash that blows/is thrown on their properties- is it fun picking up someone elses trash, no, but hey at least do your part. I've also organized neighborhood trash pickup events, and sometimes I'll take a trash bag on my walk and pick up until it's full (usually not too far!)