Drama of Systems and Morality
D&D is an experience machine. Through role play, we get to be adventurers: People imbued with more power, responsibility, and choice than your average citizen. If you so choose, D&D can also be used to experience deep moral questions that permeate our society.
Strength and Charisma
If melee characters get to use strength mod on Intimidate checks, why no similar case for the Bard to attack with charisma?
Plot Armor For Dungeon Masters
In D&D, if your monsters are not perceived as a credible threat, then it detracts from the overall tension of the story.