Yes, and it’s a fair point - but a lot of those 88% not in the city proper DID move from somewhere else, and they DID choose to live outside the city proper, for reasons of schools, finances, commute, or various other reasons. I was one of them.
In my case, it was about minimizing my commute, which was 10 minutes one-way living in NOVA and would have been 40-70 from anywhere in DC, and having 3 dogs.
As near as I could determine at the time, it is literally impossible to find an apartment in DC that will allow you to live with 3 dogs. Plus you won’t have a yard then, and would have to be manually letting them out all the time, so having a house with a yard was a big priority for me.
But everyone’s situation is different - it doesn’t seem fair to rag on suburban-livers as unrepresentative of an area when for the metro area’s population, the core-urban folk are only 12% of the population, and a lot of that 88/12 split was by explicit choice (because it seemed like everyone there was a transplant from somewhere else when I lived there).