Well you obviously want to be discrete about having that kind of cash in your home. I am sure they were not advertising the fact that they had cash.
His wife also mentioned her testimony against civil forfeiture laws that the money was taken from various parts of their house and from their safe, which implies that they had money hidden in multiple places, so if they were to get robbed then the criminal might find some small amount of money, take it and then leave.
Without additional information my suspicion is on some marital problems or addiction or something other cause that I can't think right now. Money hidden in multiple places at home? With young/early school-age kids living in that home? It just doesn't compute. Kids at that age are so nosey that you cannot hide anything from them, if you raise them normally.
The fresh-flower market that I've mentioned before had one/two nearby jewelry/watch/buy-sell-gold kiosks. One day one of my elementary school classmates came to school with gold bars and started giving them away (I'll say 1/4M$ at the current prices). Some observant janitorial/custodian lady collected them back and alerted the administration. The real reason was alcoholism of the parents of that kid.
People and families handling cash/cash-equivalent-valuables have everyday rituals that assure their safety, mostly from common crime. I just can't seem to find such "safe-normalcy" I would expect in the BurtW's family or any other family that lives with and runs cash-intensive occupation.