Why nationalized banks doesn’t provide loans to DMC approved constructions & how much is safe to buy such home?

Why nationalized banks does provide loans to DMC approved contructions and how much is safe to buy such homes with loans from co-operative banks.
Also many of the buildings which are not having OCC and CC (certificate of completion).
Still those properties are sold and bought in real world.
How much is the risk if we buy some property which did not have OCC and CC?
This is regards to properties in Dombivli town of thane in maharashtra