Why did firearms make traditional plate armour thicker and heavier?

The development of hand firearms in the 16th and 17th centuries fundamentally altered the role of plate armour. As projectiles from weapons like the harquebus and musket became more lethal, armourers were forced to increase the thickness of the metal plates to provide effective protection against these high-velocity missiles.12

This necessary increase in thickness directly resulted in a significant rise in the weight of the armour. Eventually, the weight required to stop such projectiles became so substantial that it rendered full suits of plate armour impractical for active military service. Consequently, plate armour was largely abandoned in favor of increased mobility, eventually disappearing from infantry use by the 18th century as its cost and weight outweighed its protective effectiveness against contemporary weaponry.12