The whole point of Ascension Island is to be challenged. xD There's a reason they don't let you use your wings there. ;)
If you could just fly up, Sky's Rim wouldn't be much of a mystery, and the fact that Feral Heart included a small challenge like this just goes to show that they put time and effort into creating a game like this. Reaching the top of Ascension Island gives one a sense of achievement, as though they've accomplished a great task.
In my personal opinion, I know that Feral Heart isn't exactly a "game."- There's no real goal, highpoint to achieve, enemies to destroy, highscore to beat, or anything like that, so I find it quite refreshing to see a small obstacle to keep the game interesting. :)
If you'd like help reaching the top of the Island, just press the feather quill (or press the "B" button) and go to your homepage options. Once you've reached a point at which you're satisfied, select "Set Home." The next time you fall, select "Go Home" and you will be taken back to the point you saved your home as. (Be sure to consistently update your "Set Home" as you go and it will be a lot easier!)