Why are prokaryotes, earlier than others arising in the process of evolution, widespread at the present time?

Prokaryotes spread throughout the Biosphere, including environments with the most extreme conditions (oxygen-free environment, permafrost, high humidity or dryness, high temperatures, etc.). They are well adapted to these conditions. They have few competitors. The struggle for existence and for food is reduced. Huge density and abundance due to the microscopic size of individuals. In general, the rate of their evolution is significantly slowed down (but not stopped).