Let's rewind to look at your historical perspective properly this time.
In theory yes a court could get access to your papers but for the average person because person to person interaction produces no permanent record and what limited record is created by correspondence isn't nearly as permanent because it requires one to take the time to file it and manage a very finite space nothing anything like your present digital life would ever come to exist to be requested.
As important is the cost of such a request. Compare the risk and expense of actually spying on a large population, to the cost of tapping their phones and paying someone to listen to a million boring conversations to the cost of bugging everyone's communications at once with a box installed for that purpose.
If you consider how feasible it would be to obtain that much privacy invading mostly useless intelligence it wouldn't historically have been hard it would have been impossible. They could have flown to Mars easier than doing that much physical surveillance unless every third citizen was spying on the other 2.
Historically I suspect such requests to logically be rare outside of settling business matters where receipts and contracts would be common or wills/trusts.
If you want to justify some sort of key escrow system you shall not find justification in returning to some hypothetical state of nature that never was.
Neither mass use of unbreakable encryption nor mass surveillance enabled by court order, nor your suggestion bear any resemblance to historical reality.
Furthermore if we can't trust the government not to break its own laws what would keep them from simply ordering your keys confiscated and ordering whomever holds them not to tell you?