You are correct regarding the independence of lines.
In terms of why we do it this way: Hookpad is a musical sketchpad that borrows elements from DAW’s (Logic and Garageband) and classical music notation composition software (e.g. Finale and Sebelius) but also draws much of it’s inspiration from familiar text editing we all know and love.
The concept of a line doesn’t exist in DAW’s but deleting notes does not cause the rest to shift over. Similarly in scorewriter’s like Finale, there is an independence that is respected between measures. Music isn’t text, and having some things stays in place (to a certain extent) makes a lot of sense.
At the same time, text editing is something that feels incredibly natural and intuitive to most of us now and applying this scheme to music entry is one of the things that makes Hookpad so unique and is integral to its being approachable and intuitive.
This is the design choice we made: Shifting within a line like text, but no shifting between them (DAW’s don’t shift at all, Finale shifts between measures).
As you have discovered, there are a few compromises. If you delete a few notes/chords from a previous line and want the notes from the next line to take their place, you need to use cut and paste to grab the measure you want. You can also resize the line to remove that measure. Hookpad is designed for scoring individual sections so this is a quick change.
That said, we would consider the addition of an option to turn on “full wrapping” in the future if there is enough agitation for it, but you might find it surprising how awkward it would be to have the entire song shift when you delete a note. There’s a reason the other editor’s don’t do this.
As for the issue of not being able to span a note across multiple lines. This is currently the case. There is nothing in principle preventing us from implementing a “note tying” future just as is done in traditional music notation. Time and our strong desire to keep from cluttering the interface with confusing not well thought out features are the only things keeping us from doing this. It’s on our list. In the meantime, we recommend choosing your line breaks on measures that don’t have syncopation or, failing that, cutting off the duration. The note won’t sound quite as long as you intended, but can be fixed when recording the finished song (Hookpad isn’t designed for creating polished finished music. It’s a music sketchpad for getting your ideas down on paper. Ryan’s latest songwriting video shows how Hookpad is meant to be integrated into the workflow of writing a song from start to finish:
Hope that answers your question. It’s a good one!