I think that was very common at the time (and even still today), where directors and producers get the idea that they can "fix it in post." DS9 was created at a time where it was becoming easier and cheaper to correct mistakes digitally after filming had completed.
That doesn't really answer the question as to "why" they decided to not "do it right" while filming, but it was pretty common in many TV shows and movies.
For example, look at almost any of today's movies FX reels and there will be what appears to be needless CG manipulation. An example I see over and over is a scene outside, in a park or otherwise, where their may be a bare spot in the grass, rather than spend then $25 and half an hour of work to patch in a new section of turf, they spend X thousands of dollars to "fix it in post" and go in and paint in the grass, frame by frame.