WN doesn't have status passengers so if you preboarded on WN it is due to you requiring extra assistance (toddlers, elderly, etc). Those people would generally be excluded under other rules but this stops people from claiming a need to preboard just so that they get first dibs on the exit rows since there is no assigned seating.

WN is known to be very lenient when it comes to preboarding so this just stops a bit of abuse.