There are only 2 reasons I gathered:
1. They think showing their love spoils her and could take him easy.
2. Showing affection is some weakness.
Man, showing your affection to the woman you love is not a weakness at all. If you only knew - A WOMAN WILL CARRY THE WHOLE WORLD ON HER SHOULDER FOR THE MAN WHO LOVES HER.
To the Gentlemen: Would you consider this as a weakness? Why?
To the Ladies: Would you carry the whole world for the man who loves you?