I think a lot of it is the high intelligence of crows. If you feed say, wild deer or other animals they become dependent on humans to survive or end up sticking around human areas. Crows are already everywhere and their intelligence means that if the food source stops, they can still just do their thing. It doesn't disrupt the ecosystem though it can make them into an annoyance for neighbors.

The more we learn about crows, their behaviors etc the more we realize that we severely understate their intelligence with each new finding.