Who are going to leave your private key with who? On paper will you leave at home or with your attorney? 

Family, burglars, bad friends, if you leave it at home.   And maybe your lawyer might just decide to cash in.  There will be no trail to follow them.  Could leave privkeys in  safety deposit box, but then will have to make sure your beneficiaries get the key.

Some people may live in countries that have limited legal protection when you pass so this locks it into the blockchain.  In reality smartcontracts are made for this type of application.