What most people want to do is just collect a bunch of ideas and eventually turn them into something new.
Moving around text is really hard because text selection is hard.
Doing secondary actions on a paragraph doesn't work because it would cause the text to select. You could click on the bullet, but this would be likewise difficult and counter intuitive and tricky.
Trying to insert your cursor between two paragraphs is hard(ish)
Roam is all about combing information and doing some serious transformations on them, mobile doesn't offer much screen real estate to see much information at once.
Searching by typing is awkward, although perhaps still the most accurate.