Chocolate is much harder, both in the growing and the processing. Coffee can be a houseplant because it can flower and fruit at shrub size. But cacao needs to grow up into a full sized, very large tree to produce. There ARE places that sell cacao seeds, but given how recalcitrant they are and how quickly they spoil once cleaned, you're probably better off going to someone who sells exotic fruit (or a fancy supermarket that does so) and buying a whole pod.
And, even if you CAN get pods off your tree, it takes a lot of effort to convert those beans into cocoa, let alone chocolate. You have to ferment them, dry them, roast them (usually) grind them, add the sugar and stuff, conch them (the process that makes chocolate creamy, without this, chocolate is sort of granular and crumbly, like those Taza bars or the "hockey pucks" they melt for Mexican hot chocolate. mold them and let them set. A lot of work for what would presumably be a very tiny amount of chocolate. Even the white pulp around the beans (which is very tasty, and a pickers perk) isn't really enough to justify the labor for an individual.
It's sort of the same reason I have never considered growing my own tea. Growing a tea plant is fairly easy (if you live somewhere semi-milk, like Great Britain, you can actually grow it outside). But most of the magic in really premium tea comes from the special qualities of individual famous tea bushes and the centuries of skill on how to cure and prepare the leaves. On my own, I could just make basic green tea, and I don't like that.
Then again, if it makes you feel any better, I'm currently toying with the idea of growing my own nutmeg tree, which is almost as foolish as chocolate.