Over here, the government are saying pretty much what you are -- that it's primarily the fault of UK and EU businesses for failing adequately to prepare.
Both business and the Opposition are rejecting what they see as an attempt by the government to shift the blame for failing to provide business with the details they needed to comply with the new customs and regulatory regime after January 1st until just before Christmas, with the result that, while people knew well in advance they would need a great deal of extra documentation, they didn't know in detail what they'd need until the last minute, with the result they're struggling now.
I reject our government's analysis as a pretty feeble attempt to shift the blame for the results of their own bad policies and incompetence onto EU and UK businesses by telling importers and exporters that it's their fault, not the government's, that they're so poorly prepared for Brexit.
You seem take a different view, and agree, at least to some extent, and possibly without realising it, with people like Michael Gove and Jacob Rees-Mogg that it's not their and the government's fault Brexit isn't going as well as they might have hoped, and that any problems are primarily the fault of UK and EU customers and businesses failure to make better preparations, but I think we'll just have to agree to disagree about that.
To my mind, the problem is that, while everyone knew well in advance they had to prepare themselves for Brexit, and many of them did start making preparations well in advance, they weren't given sufficient information to make all necessary preparations in detail until it was too late to complete them before January 1, because the precise information about the exact preparations they needed to make wasn't available until the last minute, and I blame our government for that.