I care on a deeper level. Honestly, it is cheap to think that I have to know the backstory and personality of a couple of people to care about the survival and evacuation of hundreds of thousands of young boys. Dunkirk asks you to care on the level of ideas and not persons. That won't work for everybody, but it worked for me.
It would be wrong to make it seem like the heroic story of Billy Bob surviving the event. Dunkirk was not about a couple of heroes, but a lot of people coming together to make an effort to survive another day. It's about smaller moments of heroism that aren't bolded and cheered on by the masses.