I agree that it can be annoying, but I also agree that there's probably nothing the police or the stores can or will do. The drummers can be especially annoying, in my experience, because they're so loud and the noise seems to project better and further. Even if they're talented I don't necessarily want to hear it. And if they're not particularly good, oy.
At least they're outdoors. For me, the absolute worst was when I'd get downstairs to wait for the subway and find I'd become the captive audience for a busker. It generally wasn't music I had any interest in listening to, and of course I couldn't just walk away. Honestly, even when it was good music that I was in the mood for - rarely, but it happened - it still annoyed the snot out of me, on general principles. Except for the guy who always did Sam Cooke. He was great. Possibly because I only saw him very infrequently.
Wait, actually, the absolute worst was the buskers in the subway who would talk between songs instead of just play the stinking music. Whether it was bad stand up or their take on the news and politics of the day (or the weather!) I'm getting stabby just thinking about it.