Why are power factor correction capacitors connected in parallel with the load not in series?

Capacitors are connected in parallel for power factor correction because the real and reactive currents of a partially inductive load are not in series, they are in parallel.

A parallel capacitor will operate at the supply voltage and needs to compensate most of the fixed inductive current.

Connecting capacitors in parallel results in more energy being stored by the circuit compared to a system where the capacitors are connected in a series.

Hence, capacitors are connected in parallel to increase capacitance to increase the electrical energy stored.