What a deal! And for something that delicious, it's no wonder these snacks are so common.
All the Pani Puri vendors I've seen have the same set-up. They have their huge plastic bag of Puri, a big pot with their flavored Pani, several small containers with spices and herbs, and another pot they use to mash all their ingredients together. They serve customers by the bite. So the experience becomes much more engaging this way. I think having each of the bites made fresh adds to the intense flavor.
Street food in general is connected to the local environment. It's a wonderful way to provide fresh food fast for people in a hurry in a big city like Bengaluru. Pani Puri vendors add to the feel and smell of the city. It's much livelier with them around, engaging their passersby. They usually show up around sunset and serve people until late at night. Pani Puri is an essential part of Bengaluru night life as well.