There was a similar discussion about how research status is displayed before, though I wouldn't have been able to find it quickly.
As I recall (though I could be wrong) one of the main arguments for the way things work in the game right now was this. Estimating the state of an ongoing study cannot be completely accurate. Scientists can't measure how much of the work they've already done and how much remains to be done. All they have is a rough preliminary estimate. In the game, this is known as the cost of research and is specified in the game or mod code. That's why all further progress estimates are based on it. However, the actual progress of research can be both shortened by an unexpected breakthrough and, conversely, delayed due to unforeseen advance difficulties. This is modeled in the game by the randomization of research costs. But the scientists themselves cannot know about this deviation. Therefore, they are unable to take it into account in their assessment of the study's progress, which they report to management.
Therefore, knowing exactly how much is left until the end of the study, from the point of view of realistic gameplay, is cheating.
Maybe I'm wrong in some details, maybe I put my own understanding of the problem into this explanation, not the same as the others. But the fact is that this issue has already been discussed and most likely more than once.