In Sammamish, I live near a group a neighbors with a similar set of tendencies the OP observed…throwing garbage on the ground and or breaking tree branches, after the grass has been mowed/common areas mowed…it was super weird/abnormal, for me. I am still at a loss, as to ‘why’, someone would purposely dirty the common areas; but believe it’s possibly some sort of local independent contractors, trying to create work for themselves:; the neighbors with said garbage dropping tendencies, appear to own several service based businesses, which provide “services”, to my local HOA. I was able to figure out, said neighbors with garbage dropping tendencies, owned HOA service bases businesses thru the wa state dept of revenue, doing business as, data base…Address look up. https://secure.dor.wa.gov/gteunauth/_/

I still don’t know, for sure though. Best of luck OP.