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.
It is possible that they have some problems. I really don't see the connection between having a lot of cash in their home and being addicted to alcohol/alcohol abuse. There isn't any real reason why someone couldn't just use their credit/debit card to buy alcohol in large quantities ect.
It would make more sense if they were addicted to some illegal drug(s), although it is not against the law to be addicted to illegal drugs (it is illegal to use/possess them though).
I still don't think it would be all that out of the ordinary for a family with millions of dollars to have $30k stashed in their house. I would assume that the hiding places were out of reach of children and possibly under lock and key
Keeping $30,000+ in cash on hand when you're trading bitcoins makes sense to me. I only trade infrequently and even then almost always in amounts under $1000, but I've had plenty of traders tell me "If you know anyone looking to buy/sell $X,XXX or $XX,XXX worth of BTC, let me know." Someone who trades regularly and in large enough amounts to make it fairly profitable probably comes across such traders quite often. Withdrawing that much cash or travelling to a location outside the home seems much more likely to draw unwanted attention to me.