During the Windrush scandal, those whose right to remain was under threat had legal status but were unable to evidence their rights, leaving them vulnerable to harmful hostile environment policies.  
EU nationals and family members who do not apply under the EUSS will be left with no legal status whatsoever.  
After the EUSS cut-off point far more people will fall out of status, with similarly devastating real-life consequences to those faced by the Windrush generation. Granting automatic settled status is the only way to avoid this.