What? The author of the bot releases the bot for a price. So they make money because they've made a product which has value. You know, like everything else in the economy: you create something, it has value, you sell it.
Well said, @tepiero. Another important viewpoint to consider is the stability of the income. While the bot might make a lambo overnight, it might not. Although you could increase your profit with fine-tuning the settings, it is riskier than having a stable business process that sells your virtual product, like a bot, for a fixed price.