Why then is it only found incorporated in sediments? There are some types of metamorphic and igneous rocks porous enough for this, yet it´s not observed.
Why then are hydrocarbons observed on other planets? How did they come to be?
Oh, I wouldn't say that. Way back when, the U.S. and the Russians were supposed to fight a war over Middle Eastern oil fields because the Russians didn't have any oil. Didn't have the 'correct' sedimentary layers for oil deposits, 'they' said.
Of course, Russia is a huge oil exporter today because they went for the deep, abiotic oil. It's probably biological oil that is the fairy tale. More likely that oil is abiotic and biologically contaminated rather than biological in origin.