Geothermal energy has many disadvantages.  Among the most important are:

• It is only available in a very limited number of places.  It can only be viably extracted from a few places where there are heat sources very near the surface.
• The energy must be converted into electricity on the spot.  It is not like oil that can be shipped from one place to another and used at any given spot.
• The costs are very high.  Someone who wants to exploit geothermal power has to build the equipment needed to tap the heat, but then also has to build a power plant and electric lines to connect that plant to the grid.
• These are the main reasons why geothermal energy is not used very much.