The study followed an aggressive push by the Pentagon and the Obama Administration to expand female participation on the front line.  This included the much hyped inclusion of women in Army Rangers training - The program was later exposed for giving special treatment to the female trainees and lowering their fitness standards.  In essence, it was the beginning of DEI within elite units in the military.

However, the Marines study relied on merit based standards and was not skewed to make the Pentagon brass happy.  It told the truth:  Women and mixed gender units offer dismal performance in the field under pressure.

Data collected during a months-long experiment showed Marine teams with female members performed at lower overall levels, completed tasks more slowly and fired weapons with less accuracy than their all-male counterparts. In addition, female Marines sustained significantly higher injury rates and demonstrated lower levels of physical performance capacity overall, officials said.  Any unit with women was dragged down.

DEI is a disaster for most endeavors, but it is especially deadly in the military where performance and merit determine life and death.  It also causes divisions and distrust; if a soldier cannot be counted on to perform tasks to a certain level of expertise then they can put the entire unit at risk.

Furthermore, women would likely act as a distraction in the field and in combat for a number of reasons which should be obvious to anyone with half a brain. 

These same concerns are practical and apply to any fighting force around the world, they are not specific to the US.  That's why it's disturbing (but not surprising) that the British government is now holding soldiers under their "Terrorism Act" for questioning the idea of women in combat.