An opportunity to seek vengeance on their friends behalf; the socs wanted to avenge Bob's death, and the greasers wanted to settle the score for Johnny.
Also, the lot is a less conspicuous place where they hoped cops would not break up the fight. Moreover, the lot is convenient for the greasers in terms of location because it's their neighborhood.
Because the status of National Park comes with federal protection and funding to go towards conservation. Even if there aren't that many visitors, tourism still creates revenue to go towards maintaining America's wild lands.
It might help if we could see what the paragraph and choices were :)
