Let’s cut the pretense that this is somehow an unexpected outcome that needs any explanation beyond ‘Brexit’.
The impact of Brexit on cross channel traffic was widely predicted (refer your ‘Project Fear’ files).
The British Government knew it was going to happen, they built massive lorry parks near the ports in readiness for the delays they knew Brexit would cause.
Nor are these delays and jams new, they’ve been happening daily since Brexit, they are in the news now because of the scale of the problem over a couple of days, but they are now routine in cross channel traffic.
The bill for this Brexit created costs and delays is being paid by the UK economy.
And it gets worse.
The UK have not yet implemented the border controls that Brexit necessitates.
There is absolutely no reason why any EU nation needs to check goods arriving at their own borders if those goods are destined to be shipped directly to the UK. (Their duty to do so was removed with Brexit).
By example, a container can arrive from anywhere in the world at a French port, then be put on a lorry without being checked and trucked across The channel to the UK, where it won’t be checked.
No taxes and duties being collected, no safety/security checks.
The UK got its borders back, then immediately lost control of them.