Why are denser fuels like $ ext{RP-1}$ often favored for the first stages of launch vehicles?

Answer

They allow high thrust to be packed into the smallest structural envelope to overcome gravity.

The initial ascent demands brute force and overcoming gravity, favoring high density to keep the first stage structure compact, even though $ ext{RP-1}$ has a lower $I_{sp}$ than hydrogen.

Why are denser fuels like $	ext{RP-1}$ often favored for the first stages of launch vehicles?
hydrogenfuelrocketpropellant