Because cleaning nature make you see directly the impact of your waste on the environment, and how much effort it is to clean, to recycle and get rid of trash.
Also, you will certainly notice a change of mood and a shift of consciousness. Toward cleaners of all kind,that do the work of keeping streets and environment clean.
It will help you connect again to nature in a era of hyperconnectivity with low deep connection to earth.
You will go outside and will certainly enjoy more your your walk in the park cleaning it and resting after than just walking in park ( but that's depends on you )
And finally, lower guilt toward the trash you find outside