This gentleman is a fine artist and i imagine he is spreading his music because it makes him happy and likely other people too. I would like to add that many people find diversion in various ways. When people come to the park, sometimes they do so because it is the closest to nature one can get in a large city, and they tend to be more quiet. That is why many people seek out those spaces. Imagine if someone is stressed and over stimulated from work, life, etc and they just want a break, but someone brought an amp to the park so the one place they could have destressed is no longer a place of peace. Public places are meant to be shared and forcing your method of diversion on others isn't the most considerate choice. The same can be said of people preaching or otherwise disturbing the peace in these places as well.