Do you route traffic through WireGuard or OpenVPN? I am not sure data limits, when distributed across hundreds of relays would be prohibitively expensive. Your data is paid for from the initiation of the connection. Them passing it along using Wireguard is not too much by my estimation.

Think this way: If you were to try to extrapolate your energy costs to corporate bitcoin mining you'd think "There's no way they could make money" yet somehow they do. (They get better rates than you)