I feel like it's harder to get good news via inquiry because usually the lag time between the committee making a decision and notification of acceptances is very short compared to notification of rejection. In addition, from gradcafe histories, it seems like acceptances tend to come out before rejections (for most schools), meaning they don't hesitate to email/call accepted students but seem to wait a while longer before notifying rejections.
It would make sense for them to do it this way since there is a bit of work and logistics for accepted students -- notifying, giving details on finances and visits, setting up the visit, forwarding the application to the Graduate School if necessary etc.
I also think even if there were say 10 spots, and from a first meeting, the committee already decided on the top 5 spots and were going to meet one more time to debate the last 5 spots, if you were one of the top 5, they still wouldn't let you know the good news upon inquiry, because it's really hard to "take back" an acceptance. I would guess that they would wait until they finalized their first/next wave before notifications. And it may also again be easier logistically to process all accepted students at once.
So I think that's why it seems like you can only ever get bad news upon inquiry. But this means that the inquiry process itself isn't "getting you rejected", the inquiry just sped up the same result. (I guess an inquiry could cause an immediate rejection if you worded it really poorly or something!)