Not sure what you mean. The military was the last one out from the evacuations as far as I know, on Aug 30th. And that withdrawal had to be done by a timeline already extended from the Doha accord, to Sept 1st.
While the whole mess is deeply regrettable and while the evacuations were chaotic, too late and insufficient, I don't see how the US could have kept troops in country to allow more civilians to leave past that deadline. The thing to keep in mind is that the rapid collapse of AFNA took a lot of people by surprise. Yes, there will be people who "saw it coming". But leaders who see a collapsing situation can't be open about it to the troops and the country at large, that would accelerate things even more.
And once it got started, it assumed a momentum of its own. Not many AFNA troops were going to die fighting just to cover the withdrawal of others.
Now, of course, Biden could have repudiated the Doha agreement, to achieve what you seem to aim at. But that is opening a very different can of worms. And keep in mind that, as much as Biden was on record as early as 2011 to want to minimize US presence in Afghanistan, Doha was not agreed to by him, it was agreed to by Trump.
Probably the best bet now is for the US and other Western countries to keep on diplomatic and economic pressure to get the Taliban to allow the people they don't like to leave and resume refugee evacuations going forward.
p.s. You can always read the full text of Doha, 4 pages, with multiple copy-pastes of "the Islamic Emirate of Afghanistan which is not recognized by the United States as a state and is known as the Taliban" occupying a not-insignificant proportion of those 4 pages. Not exactly the poster child for "best deal ever" obtained by US negotiators. I expect most people's rental car agreements have more clauses in them.
p.p.s. who is this Berman fellow and why should we care about his opinion? Is he this guy? If so, what are his credentials for second-guessing the military on how to conduct evacuations? I fail to see too many here.
Russell A. Berman (born May 14, 1950)1 is an American professor of German Studies and Comparative Literature. He is the Walter A. Haas Professor in the Humanities at Stanford University.2 He is also a senior fellow at the Hoover Institution.3 He is the director of Stanford's Thinking Matters program. He previously served as associate dean and director of Stanford's Overseas Studies Program.
Born in Boston, Massachusetts, Berman received a Bachelor of Arts degree from Harvard University in 1972 and completed a doctorate at Washington University in 1979. Since 1979, Berman has been on the faculty at Stanford University. In 2004, he became the editor of Telos, a quarterly journal of critical theory which has included extensive discussions of the Frankfurt School as well as Carl Schmitt. In 2011, he served as president of the Modern Language Association (MLA).
Together with his protégé David Tse-Chie Pan, he served on the U.S. State Department's Commission on Unalienable Rights convened by Secretary of State Mike Pompeo and led by Harvard professor Mary Ann Glendon.