Reason 1 - Running on default
In life, it's way too easy to run on default (the two sweetest words in the English language). We're programmed to follow what everyone else does. At one point in our history this made sense when that could mean life and death. Today, most of the time it means leading a boring life full of keeping up with the Joneses. By putting this list together and choosing things that are outside of my comfort zone, it forces me to do something new.
Reason 2 - I'm a goal driven person
This is the easiest reason for me. I do very well with structured goals. Without them, I tend to flounder. By putting together a solid list of goals, I am encouraged to do something new and exciting all the time.
Reason 3 - Experience all the things!
I view life as a collection of experiences. While it's nice to have in-depth experiences, that takes a lot of time and dedication. I prefer to just experience all the things. As I experience new things, new paths unfold before me. With this list, I have no real plans of diving deeper into any of these things (well, except for the ultra marathon). But I'm open to becoming enamored with something on the list because of how it felt, and I'll go down that path to experience more.