Because planets are round.
Humnn,,, I have thought more about this and come to the conclusion this is actually because the Flight Assist wants to keep you going in a straight line while the planets are round. So,, the only way to go "around" a body is to keep pushing the nose down. (OR up when doing a glide search.)
Now the question is,, with FA OFF would you be able to set up a macro that applies UP THRUST so it wouldn't be necessary to keep pushing the nose down? Probably have to be a combination.
OR
Since I was able to write macros to do the "GLIDE SEARCH" and hold the ship at -5 to -7 deg pretty consistently to get maximum distance from the GLIDE, I think I could write one that would hold the nose at +5 to +7 deg to go around a body while getting maximum distance for the least altitude gain..
In any case, my experience with the GLIDE CORRECTION MACRO was that the PITCH DOWN command time delay to hold a constant negative angle got shorter as the altitude went down. (The smaller the radius is, the shorter the arc becomes for the same angle. If speed is constant, then time to travel the arc distance gets shorter.)
Current thought is that a macro to automatically do the nose down corrections would be much harder to work out (or there would have to be several of them based on the distance desired.) because every time I went to a new body with a new radius I had the recalculate the theoretical maximum glide distance from the TICK where the scanner started to register to the minimum glide altitude (usually about 5 KM) and then change the time delay between the pitch down commands.
For the NOSE UP macro there would be two variables.
The arc distance for each degree of change
AND
More difficult to program for, the speed of the ship and therefore the time to travel the arc distance.
Easier I think to be able to do what I currently do. Switch between digital and analog controls and simply tap the pitch down key as needed to hold the +5 to +7 deg path.