Why is lust more intense than love?

Smaller flames tend to burn longer.

it's more primal, lust connects directly (and only) to the lizard brain, down below where we do what we like to consider 'thinking'. Love is less visceral, less connected to scent and immediacy.

To me they are two sides of the same thing and lust is temporary but love - hopefully - lasts.

Because it usually involves something we know we shouldn't have but want it anyway.

Oh yes!