It's exactly what I described in point 3 as 'the problem'.

Maps 'work' because as a programmer you're aware of how expensive it is to copy a whole hash table, and it makes sense that a pointer to the thing is the whole thing. So it's an exception, but one _clean_ exception that just behaves consistently.

Slices are horrid in that they SOMETIMES work the way someone who passes by value expects, and that's the same for both NOT updating AND Updating. This is because the management stage is passed by copy, not reference, but the backing data IS a reference, which initially is copied. That leads to in-place overwrites when no change in size has happened. It leads to appends that do get written but not reflected in other copies of the slice, and then if there's a need to re-allocate it leads to even the updates not updating the other copies of the slice.

Slices are the most beginner un-friendly part of Golang.