Why are capacitors with large values are manufactured polarized?
Capacitance is  dependant upon; 

(1) the area of the plates, 

(2) the inverse thickness of the di-electric or insulator between the plates 

(3) the permittivity of the di-electric or insulating layer. 

To make large value capacitors which don't require enormous plate size you need to have a very thin insulating layer with high permittivity. 

Electrolytic construction requires the capacitor to be polarised to maintain the insulating oxide layer created by action of the electrolyte on the metal.

Reversing the polarisation will destroy the insulation and create a short circuit.



N.B. Unpolarised capacitors can be made with high values but will be be physically larger than their electrolytic companions value for value.