Why did the man react so strongly when he saw us cleaning the sidewalk

Hello everyone. Today our group continues to clean up the weeds and collect trash in the park and recreation area of ​​the people in this neighborhood. The people we met here all said it was a pity that the park and recreation area for everyone was not taken care of and cleaned, causing weeds to grow and there was a lot of trash here. When they saw our group doing the volunteer cleaning work here, many people had a reaction that surprised us when they did not believe that someone would come here to do this work voluntarily. We invite everyone to follow our work process and contribute more ideas. Thank you. #cleanup #grass #help