Because it works. Its simply experimenting with different reactions until achieving the desired effect. I want to communicate disinterest in buying from stree

Because it works. Its simply experimenting with different reactions until achieving the desired effect. I want to communicate disinterest in buying from street vendors. I try various forms/styles of communication until I accomplish my goal. I've had this problem in the USA, and merely looking unfriendly is often sufficient. In your situation, that's clearly inadequate.