Like any other server, a proxy server app has its technical characteristics: response time, connection speed, cache size, etc. The better these characteristics are, the more convenient it is to use an app. Logically, no hosting provider will provide its equipment for free. Building your infrastructure, connecting an access channel requires money. Payment is compensation for all costs, including the margin of the one who provides this service to you. Due to the availability of payment, companies can guarantee decent bandwidth and performance.