In order to fulfil their purpose of giving a place for large mammals to live naturally, many national parks and nature reserves are very large. Often this is a great draw for tourism, and when done right can create a healthy income for many people living in the area around the park.
However, this area is also a something that often takes a great deal of time to drive around, adding cost for the rest of the economy and so often the road is built across the park. In the short term this can often appear like a good idea, but can have serious problems.