I understand your concern but how hard would it be for the Glock company to modify the Glock 19 to add a thumb safety in order to fulfill a military contract. Personally, I think a safety on a handgun diminishes its effectiveness given that it is a purely defensive weapon, especially in a combat environment.
A frame safety is the one thing I wish all my Glocks had!
Personally I think the trigger safety is more of a drop preventive or unintended contact deterrent. I just don’t like the sole safety being like it is.