I agree with your original statement to some extent. If Chris had lived to write his own book, it may or may not have attracted wide attention. You would think it would be better than Cheryl Strayed's "Wild", however, which has achieved moderate success.
I don't think this takes away from the unique nature of the man. I have traveled extensively around the U.S. over the past few decades and encountered most types of alternative culture that you can imagine, but have met very few people who live out their philosophy and put their money where their mouth is in the way that Chris did. I can think of one young man for comparison who is similar, but stayed alive. His name was Paul G______, and he was from Massachusetts. I met him in Missoula, Montana in the early nineties, and he had traveled there by bicycle from the East Coast. He just had one small bag and bedroll on his bike. He mainly lived off peanut butter and jelly sandwiches and had many stories of his adventures from multiple times crossing the country. He also was a devotee of Thoreau.
Paul's story is unknown, even though I find it just as compelling as Chris's story. He was educated and raised in a similar way, etc. I have seen comments that there are many kids like this, and Chris is only famous because he died, etc. I do not believe that is accurate. There are many hobos who are destitute for different reasons. There are very few people who see the flaws in society and consciously abandon everything to live a more authentic life and who actually live by their ideals.
In other words, we know his story because of his death, but his story is far from common.