Question

why are manures considered better than fertilizers

Answer 1

Because they are made naturally with the peels of vegetables etc and can maintain soil fertility

Answer 2

Manures are actually organic compounds which are made of animal waste , farm waste etc.
They are rich in humus
Manures do not pollute the water the water resources
Excess use of manures do not destroy the crops ,whereas excess use of fertilizers destroys the crop as well as the soil

Manures are not expensive as fertilizers