As I understand what happened with the Corralito, it wasn't just a simple pesofication, but rather fraud committed on the people by the the government under the guise of legal operations. My first introduction to this was my barber, who had a Dollar account, and a mortgage on a house denominated in Dollars. The government declared a conversion to pesos from dollars everyone's account and within a day or so the value of the peso went from 1-1 with the dollar to 3-1, which resulted in a net loss of some 66% or more of his (and everyone else who had Dollars) actual value. With his mortgage, it was denominated in dollars when he took it out but the conversion took place 1-1, effectively raising the cost of his mortgage times 3.
Both things seemed quite strange to me, but I've had a number of other Argentinos confirm that they were affected like this as well.
Therefore, to answer the question of the thread, one reason why people here keep their savings in a metal box, or under their bed, or buried like treasure (I know someone who does this!), it's because they don't trust their government and the banks.
Of course, I don't believe for a moment that Cristina, and her children as well, are innocent of robbing the State, but this money was so obvious that I think they can probably explain it or Florencia may not have been so insistent that the government come and inspect her safety deposit boxes and such. But either way, I do find it interesting that the ex-head of state and her children apparently didn't trust the government enough to keep it in a savings account...they must have known something about trustworthiness, or the lack thereof.