My answer to your question is that I honestly don't know why. I think we start reading each other's numbers and either start to feel a little competitive when we see numbers in the 4s and 5s, or want to be just like everyone else. It's schooldays all over again.
But everyone is an individual. Different blood groups, different BMIs, different genes, different lifestyles. Different types of diabetes, for that matter. Yes, I am happy with my 5.9 this morning because it's lower than some other numbers I was pulling earlier this week. But I feel well, the way I am eating seems to agree with me, I am still losing weight (slowly), and for all I know the switch from one SSRI to another two weeks ago has affected my BG numbers.