It's a loss leader, host the Pi for free, then sell the reboots, SD card swaps, extra bandwidth, IP blocks.... Eventually upsell the customer to a full hosting

It's a loss leader, host the Pi for free, then sell the reboots, SD card swaps, extra bandwidth, IP blocks.... Eventually upsell the customer to a full hosting package if they had used the Pi for an extremely cheap hobbiest/project/dev environment before going to a real server.