I believe that it had something to do with it being relatively much work to update things deep in a tree.
Like, if I have Model -> Users -> User -> WallUpdates -> WallUpdate -> Comment, and I want to make an update to a comment, I'd have to do a lot of code writing. Is that true, or did I just miss the magic function that helps me do this?
But I'm now realizing that maybe, if I want to "manually" do that, I'm just doing it wrong - this should partly be what Om's cursors are meant to avoid, right? (this, and locality to components)
In general, if it helps you as feedback, I found Mori a little difficult to approach, having no Clojure experience. I suspect that some more examples of typical usage patterns at the top of the docs would do a lot. Like, which methods are supposed to be commonplace, and which ones are more for edge cases? What kind of things am I supposed to do all the time, what kind of things should I wish to avoid except in these and these cases?
FWIW, I feel like the same holds for Underscore/Lo-Dash's docs, except it's been less of a problem for me because I'm more familiar with typical usage patterns of mutable data structures.