The flag thing is a more recent military tradition. You salute your flag and hymn like you salute your top officer, while still showing your power as a unit, not breaking a tight formation you are standing in. Kneeling down is for their enemies, our obviously good boys share the common cause.
Traditionally one stands for the flag out of respect so not doing so is seen as disrespectful
Whereas kneeling (and bowing one’s head) for the cross is seen as basically submitting yourself to the will of god
So basically traditions being traditions, things are weird
The flag thing is a more recent military tradition. You salute your flag and hymn like you salute your top officer, while still showing your power as a unit, not breaking a tight formation you are standing in. Kneeling down is for their enemies, our obviously good boys share the common cause.