[technothrasher]

Isn't it better to keep the heat trapped inside the system and generate electricity from the pressure only?

Steam engines are old technology. They've been replaced by modern steam turbines, in which the steam is either cooled and recirculated, or used for other processes, or both.

Geothermal steam turbines typically use a heat exchanger and release the original steam, as geothermal steam tends to be very corrosive.

[jacquesm]

Steam is very corrosive in general.