Because on public servers you generally don't want all pings to be broadcasted to all players.

New plugins/PingWheel/config.yml (or similar) file would be introduced with force_ping_channels: false field. When set to true, player would be required to configure their channel in order to send pings.

As Default Channel Mode is an official feature of the Ping Wheel mod, I will implement it* when I have some spare time.

*: disabling the global channel aka "forcing a channel"

Thank you for your suggestion!