We can take this concept in increments of a decade. How do you think the % of completion has changed as the decades click by. I want to look at it from a percentage perspective to eliminate increases in population. We all understand that population on trail increases as time goes on, so to say that there are "400 more completions in 2018 vs 2017" doesn't really tell us anything more then a whole lot more hikers attempted it.
What I want to look at is this:
In 2018 4000 hikers started, and 400 finished so 10% completed the hike.
In 2008 2000 hikers started and 400 finished so 20% completed the hike.

Thus over time, more people attempt, but a fewer percentage are successful. I understand that this will most likely be speculation and opinion which is fine but if anyone is capable of digging up concrete numbers that would be fun as well.