It catches your attention.  And it's the concept that any attention is good attention. 

Bring attention to yourself and drown out everyone else. It's actually pretty brilliant.

yes..this is really ridiculouse...I've noticed the more small towns the more they do this....so if I ever noticed it in Beijing, I know the owner of this shop is from small town...I will not go their shops at all...

Probaly the same reason why they talk so overly loud.

They want attention in the most childish sort of fashion.

I usually don't go into those stores. I don't like loud obnoxious things.