Well, to large extent I guess I’m just reflecting what I perceive as a pretty strong societal convention, and I see no great personal gains to be had by defying that
convention.
We make enough that we consider ourselves quite comfortable, and we are sufficiently frugal that we consider ourselves quite secure. But we live in an area where the norm is to drive multiple BMWs/Mercedes and own $1 mill+ homes. It impresses me that a lot of these people try to openly display their wealth, almost like birds displaying plumage. What has been apparent lately, tho, is that altho many of my neighbors are quite wealthy, several others were leveraged to the hilt, and foreclosures are not at all uncommon.
So what is the benefit to my letting anyone in my neighborhood know exactly what I make, or how I have saved/invested it? (Actually, at present there are times I almost feel like bragging about how comfortable we are given the current economy due to our conservative habits, as I see people who used to spend cash like water suddenly try to come t grips with not being able to simply buy whatever they fancy. But I don’t really like my neighbors!) 
I have exactly 1 friend that I speak completely openly with in terms of income, net worth, etc. I occasionally muse at the fact that with so many people, I know their job titles, but have NO IDEA what they might make. My one brother-in-law does something with computers. They appear pretty comfortable. Does he make $70K or $170K? Or my other BIL who was a partner in a top accounting firm. He appears wealthy, but how wealthy? Did he make $200K, $500K, or $1 million per year?
But when I find myself musing about such things, I quickly realize that I am merely curious, and have no reason to really know such things about others. How much someone makes/owns, and how they choose to spend it really ought to have next to no impact on my relations with them.
With our kids, as they became teens we started telling them more about what things cost, just to help them in their college/career planning. Basically wanted them to appreciate that they have a pretty comfortable life, and that isn’t going to be simply handed to them. If they want to “follow their dream”, they might need to expect a somewhat less comfortable lifestyle. And if they wish a certain level of comfort, they may wish to plan accordingly.
So, why is money something you think ought not be private? Is anything private? If so, what, if not finances?