Changing organizational processes tends to be extremely hard in large orgs, and I wonder how the military deals with it.
It's worth noting that this was one of many incremental changes. When I started that deployment in 2009, snipers were going out in 5-man teams. The team that got hit actually did technically consist of 8 men (as was already the SOP), but they were split into two four-man elements that took different positions about a kilometer apart. The mandate going forward was that all 8 team members had to be within earshot of each other at all times. It was the latest of many orders in the trend of ratcheting up firepower at the cost of concealability.
The incident you're talking about happened much earlier, in Iraq. I believe this article is referencing it: https://www.dvidshub.net/news/6921/former-magnificent-bastar...
It doesn't say they fell asleep, because of course there's no way to know that. It's an assumption that has been repeated as fact, though it does seem likely.