Eg: Perhaps I sold a house for €1m, or bought a winning lotto ticket, or sold BTC over the Coinbase exchange for €1m.
All of these transactions will be traceable.
Well, most of them are traceable. The lottery win will be a bank transfer and there'll be no problem there as the bank will know exactly where the money came from to fund the lottery account. The money from Coinbase less clear, while the transfer request to the bank will come from Coinbase's bank, who and where did it come from before that? As Coinbase are an exchange, they're just a middleman in this, neither the source nor destination.