Because we need to retain the breadth of functionality the API has, if you want to just scrape posts, APIs for that already exist, but i am aiming for something more.
About reverse engineering, they can change that part at any time too, and may be even more fragile as they can change that without breaking the UX, if they change the front page CSS selectors or layout for example, it will effect the UX more as it changes the expected output, not the middle end that is just raw data.
Thats my reasoning, I appreciate the input though (: