Dear student,
Well drained soils are important to ensure proper growth of plants.
If the water drains off very quickly , it can't be absorbed by the roots effectively.
If the water doesn't drain off, it can lead to growth of microbes and also choke the roots of the plants due to lack of oxygen.
Both the conditions are detrimental for plant growth.
Melon is a cucurbit, thus it requires regular moisture during its growing period.
Thus in order to ensure a proper yield, melon should be grown on a well drained soil.
Regards.