Why are gravitational, electromagnetic, and nuclear forces often called fundamental or basic forces?
These forces are called fundamental forces as without these forces humans and living organisms won't survive.
Gravitational force-we cant imagine of a living world without it ,and without this THE SOLAR SYSTEM WILL COLLASPE.
ELECTROMAGNATIC-ITS too very important as light ,microvaves,radio waves ,and etc are all its types,without theses energy won't be able to travel long distances and its the fastest way of transportation of energy.
Nuclear forces are too important because its the biggest ,and tremendous phenomemon by which a huge amount of energy is produced. The sun is believed to provider of all energies on earth and in fact the sun get energy by this phenomenon.