Question

why do cockroaches leave in dry and dump area

Answer 1

because that's their nature ....cockroaches prefer to live in warm, dark, wet areas, like sewers and basements. They often enter structures through drains and pipes. 

Answer 2

hi friend.
Every animal has its own adaptatations and habitat.
For eg camel lives in desert so it can't be seen in Antarctica.
Similarly cockroaches prefers to live in dry and dump area.
And such places are suitable for cockroaches.

hope it helps