Maybe they realized that the best tool for capturing an idea is the one in your pocket (smart phone). And carrying around a big simulated leather bound book is a huge pain in the ass. No offense to those who like to tote big simulated leather bound books wherever they go, I just can’t do it (I use paper notebooks, but not for life organization and rarely for capture).
Bullet Journal is a methodology centered on paper as a medium. Building an app is a huge mistake and deaf to the beauty of its own analog process. Learn from David Allen, Grand Master of Getting Things Done, one of the most successful productivity concepts of this generation. He is sworn to keep GTD platform agnostic and insists that it ‘works on everything.’ GTD has been my method since the release of his book over 15 years ago. I organize and operate my GTD lifestyle on Omnifocus.
Every analog process, it seems, goes digital after a while.
But you’ve got to be comfortable with what you deliver. And if paper is your thing, own it and stand behind it.