> According to Cassini data, scientists announced on February 13, 2008, that Titan hosts within its polar lakes "hundreds of times more natural gas and other liquid hydrocarbons than all the known oil and natural gas reserves on Earth." The desert sand dunes along the equator, while devoid of open liquid, nonetheless hold more organics than all of Earth's coal reserves.
Went on a bit of a rabbit hole and it appears that there is a lot of methane in the atmosphere and that gets broken down via photolysis into hydrocarbons somehow, and the methane likely is there from the formation of the moon originally via methane ice.
See Figure 2 [1]. Protons, electrons and water ions from space dissociate, in the presence of sunlight, nitrogen and methane. Those combine into intermediate-mass hydrocarbons that produce complex organics. The part we don't understand is how those complex organics, e.g. benzene and naphthalene, turn into large organic particles.
Titan's atmosphere "is a largely anoxic environment, with little oxygen to cause the termination of complex organic reactions" [1].