The reason for this is to provide a true cross-platform experience; it uses the same code to flash on Windows as it does on Linux. It also employs some techniques which make it faster than dd in a lot of use cases.
I’ll ping my colleague @mcraa who is far more deeply involved and may be able to answer any more in-depth questions you might have.
Hey @adrian_au, @chrisys is completely right.
For your other question, balenaEtcher does not add or remove anything during flashing currently, so if it is not working with dd it won’t be different (just completed faster) with etcher.