Could it be that he never checked whether all the hints he gave sufficiently narrow down the location to just one spot? That he has additional knowledge for every line, knowledge which he thinks is self-evident, but knowledge with is actually just very personal to him, and cannot be inferred?
In this case, the riddle might never be solved, and he might die in the self delusion that all the attention this raised is because he is a gifted writer, when the reality is much more sad: he was a terrible riddle author that threw away a million bucks.
It's a quirky guy who buried treasure - actual treasure - along with a riddle. That's fucking magical and fun... it's beautiful. You'd have to be pretty sad to think that "reality is much more sad" for him.
Exactly, he most definitely didn't do it for designing a riddle, he did it for the fun of seeing how people would respond and seeing them struggle and go beyond expectations.
Perhaps he's hid a million dollar treasure, and perhaps he actually hasn't. Regardless, he is probably in the black financially due to book sales alone...
Whether or not it's a truly good, solvable riddle may not be the goal in the end – could equally be that he just wanted to give people a sense of excitement and wonder. Maybe that's too generous on my part, though. :)
If I were him, the point is not a million dollars. That's trivial. It's not helping people find the treasure, that's also trivial. The point is all the entertainment to be had searching for the treasure. In fact if I had some money and time I might put together a game centered around finding the treasure. Imagine all the fun to be had and all the stories to be told about the treasure that was never found. In fact I would probably not even put any treasure out there. Just a tall tale for the ages.
In this case, the riddle might never be solved, and he might die in the self delusion that all the attention this raised is because he is a gifted writer, when the reality is much more sad: he was a terrible riddle author that threw away a million bucks.