Final answer:
Fossils usually lack organic matter because they have been buried for long periods in conditions that favor mineralization over preservation of soft tissue. Rapid burial and anaerobic environments required for such preservation are not common, and only hard tissues like bones tend to be found in unaltered form. Special cases like amber or ice can preserve soft tissues, but these are rare exceptions.
Step-by-step explanation:
Fossils typically contain little or no organic matter because the conditions necessary for the preservation of soft tissues are rare. During the process of fossilization, organisms need to be rapidly buried in a low-oxygen, or anaerobic, sedimentary environment to prevent decomposition by bacteria. Due to the rarity of these conditions and the long time spans involved, organic matter is usually broken down and replaced by minerals, leaving just an impression or the more durable skeletal components such as bones and teeth.
Fossil formation commonly requires rapid burial and low-oxygen environments, which is uncommon. Soft tissues decompose quickly unless preserved in such a way, leaving typically only hard parts like bones. Unaltered fossils are extremely rare and are usually found only in special circumstances, such as being trapped in amber or tar, or preserved in ice.
Paleontologists, who study these fossils, must reconstruct past environments and biological processes from these remnants, which are key to understanding the Earth's history and how extinct species lived and interacted with their environments.