Question: Why are threats and consequences so much easier?

I was at the opthamalogist office yesterday and a woman was in there with two of her children, one about 9 and the other not quite 3. The 3 year old kept doing things that the mother clearly found annoying and she very quickly escalated into telling him that he would go right to bed when they got home (it was 9:30 in the morning) and they wouldn't be stopping at McDonald's. The more he fidgeted and doing things he wasn't suppose to which included how he was playing with the GameBoy, the more she lathered on the consequences. It turned out that the appointment with the eye doctor was for the young child and included not only the doctor looking into his eyes with that scarey light, but also having the nurse put drops in both of his eyes several times. This was clearly a stressful situation for this child and the mother herself was obviously stressed and so was everyone else in the office. It was so clear that this little guy needed help in calming and that truly the behavior would have diminished if his mother could have calmed his stress. The nurse even asked the little guy if he was now "going to be good" for the doctor. I did resist all temptation to take the mother aside and give her some ideas of how she could help her child in that moment AND where the behavior was coming from. My guess is that every time this child has to go to the eye doctor from now on, his stress level will be elevated. My question: why do we find it easier to give out threats and consequences rather than find ways to calm a child in the moment when the opportunity presents itself?