I thought the same thing. In the age of CGI, Nolan wouldn’t even need more extras to convey the enormity of the evacuation.
Nolan deliberately did not use CGI. He wanted to go totally real life, even his ships are real, I believe French Frigate made up to pass for Tribal Class DDs, like the USS Newport News became the Graf Spee in 1956 Battle of the River Plate.
Maybe he hates CGI as much as I do. They could have CGI’d in more minorities and Frogs that way. Maybe even a rainbow flag.
Nolan used cardboard cut ours in the wide shots