Same thing happens in Madistan (Madison WI) when liberals protest. Litter everywhere on the capitol mall. When conservatives protest, the place is extremely clean afterwards.
We plan ahead, people bring their own bags, they either bring big bags for lots of people to use and/or take their stuff with them when they leave.
It’s about respect. If you respect your country or state and it’s institutions and monuments, you don’t leave your trash all over it. Conversely, if you leave trash, you reveal your inner attitude.