Why do we crave chocolate so much?

We crave chocolate because it is good! It tastes good. It smells good. It feels good when it melts on our tongue. And all of those 'feelings' are the result of our brain releasing chemicals in response to each chocolate experience. The experience of eating chocolate results in feel good neurotransmitters (mainly dopamine) being released in particular brain regions (frontal lobe, hippocampus and hypothalamus—definitions a bit later).

Dopamine is released when you experience anything that you enjoy—laughing, or watching your favorite Olympian claim the gold. This reward circuit is partially hard-wired by genetics, but it learns, changes and responds to your specific preferences based on your life experiences. This malleability of the brain is what makes each of us unique. In fact, there are supposedly people in the world who do not like chocolate.

It was originally thought that chocolate contained compounds that could activate this dopamine system directly (like cigarettes and cocaine do). Chocolate does contain theobromine that can increase heart rate and bring about feelings of arousal, caffeine which can make us feel awake and increase our ability to work and focus, and fat and sugar which are preferred food sources for humans because they are calorie dense. However, elegant experiments in which the components of chocolate were separated out indicated that just ingesting the chemicals in chocolate without the mouth-feel and taste does not decrease craving.

Source: https://www.psychologytoday.com/blog/comfort-cravings/201402/why-do-we-crave-chocolate-so-much