Absent fluids like water or lava, heat diffuses slowly through substances like rock.  ISTR speculation that those deposits may not have been at their current depth for very long (in geologic terms).  If we had come along in a few million more years there may have only been gas there.

i have heard that speculation also (rapid subsidence) but what do we really know about the fluids produced from this reservoir? there is a fine line between a volitile oil reservoir and a retrograde condensate (gas) reservoir . now i know chevron's scientists know what they are doing but the difference is not always obvious. east anschutz ranch field in se wyoming is a fine example . i dont know if they have ever resolved the issue .