As is the case with a lot of open source software: The people who volunteer their time to help build it get to prioritize what they please. The people building it don't feel your pain in being unable to drag notes around the score, and so they don't want to spend their nights and weekends building a complex feature* that they don't need. The beauty of open source software is that if you find a cohort of software engineers interested in making this feature happen, you can make it happen. But that's hard to get people to build stuff for free, isn't it?
* The feature is complex. Notes most likely have data and constraints attached to them (e.g., a crescendo might terminate on a note). What happens if you drag a tied note? What if you drag a note from one measure to another? Can you drag between voices? This is a huge feature if you want to make it actually work for practical scores.
Certainly if you have inter-note dependencies (or other multi-note expressions) things get complicated. But dragging notes or other elements can be disallowed where those dependencies exist. All I wanted to do was swap the position of a quarter note and a quarter rest, and couldn't do it. That's absurd.
* The feature is complex. Notes most likely have data and constraints attached to them (e.g., a crescendo might terminate on a note). What happens if you drag a tied note? What if you drag a note from one measure to another? Can you drag between voices? This is a huge feature if you want to make it actually work for practical scores.