The same reason that there is the same short loading screen between supercruise to normal space: they take place at difference scales and in different instances.Quick question from me: Can you please let us know the reason for that short transition?
I'm not sure why anyone ever expected the transition between supercruise and planet landing to be seamless, regardless of how it was phrased--and AFAIK that phrasing was always that the seamlessness was between supercruise and orbital cruise. Planet landing takes place in "normal" space, and merging normal space and supercruise would be a huge change to the game that was never on the table.