It’s a catholic thing…
Q.I have noticed that the casket of a veteran is no longer draped with an American flag at the funeral Mass. Why not? The service of these men and women helps provide the freedom of worship that we all enjoy. Why does the church no longer honor that? (Daly City, Calif.)
A. The Order of Christian Funerals says in No. 132 that "any national flags or the flags or insignia of associations to which the deceased belonged are to be removed from the coffin at the entrance to the church."
The guidelines of most dioceses provide that the flag is then replaced by the pall, a large white cloth draped over the coffin as a symbol of the person's baptism. Surely no disrespect for the flag or the nation of the deceased is intended; instead, the pall represents the fact that all are equal in the sight of God and that, as St. Paul pointed out in his Letter to the Philippians (3:20), our primary citizenship is in heaven.
At the end of the funeral Mass the pall is removed, and the flag can be placed back on the casket before it is carried from the church. Often, at the cemetery, military honors are then accorded to the deceased; a bugler might play "Taps." Sometimes there is a gun salute and a military honor guard carefully removes the flag from the casket, folds it respectfully and presents it to the next of kin with comforting words from a grateful nation.
https://www.catholicherald.com/faith/flag_over_casket/