It's probably worth pointing out that the Marines didn't start fielding the new striker-fired pistols until late in 2020. That document is from 2018. https://www.safety.marines.mil/Safety-Promotions/Combatting-the-Blue-Threat/
Which means that during the timeframe the document is referencing, the Marines were using the M9, a TDA hammer-fired design with a manual safety. The same one that Langdon uses.
Most likely they were using the Berretta M92FS platform
picture from Wiki
The M92FS, with the hammer down, requires a long double action pull necessary to fire it, comes with a decocker, so the ignition system is effectively de energized, it has a firing pin block, so it won't fire if dropped on its muzzle, a loaded chamber indicator, and a slide safety. It is easy to visually determine that the gun is cocked, because the big hammer is very visible. And yet, negligent discharges happen. I found a document, which indicated for the time period, that more Servicemen in Iraq and Afghanistan were being injured or killed due to negligent discharges (all weapons, not broken out by weapon) than by enemy fire. I talked to a Vietnam Veteran, and he claimed the same was true in Vietnam!
Accident rates with 1911's were such, the Army was never going to go back to some single action pistol without a firing pin block, and you would think the Beretta would be a very safe pistol to issue. And yet they still have service men shooting each other with their weapons.
And you know that it is still true, for the services have put out a number of documents emphasizing safe weapon practice. So if the services want manual safeties on their striker fired weapons, it has to be due to a desire to reduce the number of negligent discharges with the things.
What the fan boys, or product cultists want, is of no consideration to institutions with millions of dollars in liabilities, when their employees accidentally shoot themselves, or others, with their weapons.