The technology we use to harness the energy in fossil fuels is well developed. The main reason for this is that fossil fuels have been used to power our world for many decades.
2. Cheap and ReliableFossil fuels are cheap and reliable sources of energy. They are excellent types of fuel to use for the energy base-load, as opposed to some of the more unreliable energy sources such as wind and solar.
The answer is they are very convenient to use (Apex)