Why AC is generated instead of DC?

Answer 1

Alternating current is much more efficient to transmit than direct current. Using Transformers, it can be stepped up to high voltages for transmission over long distances using relatively small conductors, and then stepped down at the destination to provide high current.

Answer 2

AC generators (alternators) have replaced DC generators (dynamos) in cars because they are more reliable and last longer. That is because a DC machine needs a commutator to take the current to the armature, and this requires relatively frequent replacement of the carbon brushes.

An alternator does not need a commutator, it uses smooth slip-rings, which cause much less wear on the carbon brushes so that they last longer. In this way AC is easier to generate even though the car needs a rectifier to turn it into DC.

Answer 3

Machinery driven with any strength, usually involves rotating something. Rotating a magetic field within windings, satisfies the conditions needed to induce electric current. The rotation also causes the current to change direction with every pass, which is AC.
To 'undo' this changing field and make it DC, requires switch gear in the form of a commutator, to keep the current one way only. This is expensive and puts limitations on the power generated.

DC current, however, is very easy to make, when using methods other than heavy machinery.
Chemical energy from batteries.
Photovoltaic, from solar panels.