If Big Navy is super worried about it, they can write the reg to say Seaman Snuffy shouldn't carry the Glock 19 around with a round in the chamber unless it's FPCON Delta or whatever threshold they want.SIGs don't have external safeties either though.
And if Seaman Snuffy is carrying a pistol, he is carrying it in a holster. So if he shoots himself in the foot, the dumbass drew the weapon while on duty to start messing around with it.
There's risk in not having a round in the chamber, though. Just a different kind of risk than issuing a weapon with a trigger safety.