From article, they use the relay as a fallback if UDP is blocked.
“We’ll probably also still want fallback relays that use a well-like[d] protocol like HTTP, to get out of networks that block outbound UDP.”
“Having relays to handle the long tail isn’t that bad. Additionally, some networks can break our connectivity much more directly than by having a difficult NAT. For example, we’ve observed that the UC Berkeley guest WiFi blocks all outbound UDP except for DNS traffic. No amount of clever NAT tricks is going to get around the firewall eating your packets. So, we need some kind of reliable fallback no matter what.”
“We’ll probably also still want fallback relays that use a well-like[d] protocol like HTTP, to get out of networks that block outbound UDP.”
“Having relays to handle the long tail isn’t that bad. Additionally, some networks can break our connectivity much more directly than by having a difficult NAT. For example, we’ve observed that the UC Berkeley guest WiFi blocks all outbound UDP except for DNS traffic. No amount of clever NAT tricks is going to get around the firewall eating your packets. So, we need some kind of reliable fallback no matter what.”