Why does it have to??? I didn’t delete it.
The two parts are interrelated. Deleting either damages the startup.
Erase All Content & Settings does it the way you did (sort of), but also recreates a new Data volume connected to the System volume.
Did you Erase the volume or did you Remove it? I have not tried Removing the Data volume, but that might have been successful if startup recognizes it is missing, it may create it. You left the volume, but erased the necessary startup files.
Erase all content & settings only works on a an Intel Mac with a T2 chip or on Apple Silicon. It doesn’t erase the Data volume, per se, it deletes the encryption keys so the data cannot be accessed. This is essentially the same as removing the Data volume.