I once worked in a bookshop outside of which a man played the sax (badly) all day long, every day. It drove us nuts, it drove customers away and casual staff were hard to keep. We also had to keep the shop door closed in order cut down on the sound of the "music". Finally we discovered that other merchants were also complaining but we found there was no law against this. I guess my feeling is that buskers often presume that they are contributing beauty to the urban scene when they are often adding nothing but unsolicited noise.
I think people bus for two reasons, they want money and they think they have enough talent to warrant getting it.