It is linked to the culture and the general financial situation of a population where you grew up. I have a couple of Haitian friends down in Florida. They are sending money to families members back to the island. Kidnapping for ransom is sadly a regular hazard over there. Broadcasting your wealth or the perception you may have more than the "average" (in some part of Haiti, not the whole island) would be like putting a bulls-eye on your back.
Not to mention that if the number is particularly large, even if you aren't facing kidnapping for ransom or similar situations, loose lips could incline some bastard to rat you out to the IRS just to screw with you. Even if you are honest on your taxes and pay what you think is appropriate, what is the proper metric for taxes for BTC that appreciate in value? Do you owe the taxes at the time you convert to fiat or at the time you earn it? Are they short-term capital gains taxes or something else?
I don't really have that much in BTC as I am more or less broke, but I recently realized when the price of BTC spiked that the BTC I just kept around to gamble with is suddenly actually worth real money. I now have more BTC than fiat.