It comes down to cost
Creating a topographic map for a project can be costly. A hand-rendered topographic map is expensive (anywhere from $2,000 - $15,000 depending on the size of the site), takes about a week or more to complete, and the information may still have inaccuracies due to the limited number of shots the survey can do. Moreover, the landscape in a one-week timeframe can be dynamic, so the map might be outdated by the time it is delivered.
An aerial topographic map is significantly more expensive and often more time-consuming given the need to schedule flyovers long in advance and process large amounts of data. Potential deviations can significantly affect volume calculations, which in turn may lead to construction delays and additional costs.
In contrast, drones are much less expensive for obtaining the same data. Mapping a project site using drones costs less than half the price of a hand-rendered map, and can be as low as a few hundred dollars per scan.