Back & Forth - Why is Forth so hard?

Lots of people think it's cute, lots of people try it, few people stick with it and master it. Why? Isn't Forth supposed to be a paradigm of of simplicity? My Forth compiler can be found here: https://sourceforge.net/projects/forth-4th/ You can download it anonymously and for FREE. Most popular platforms are supported - even some old ones.