@DuncinToffee
You, the OP and others have made the assumption that if two events happen at the same time, they must be connected.
As pointed out by others earlier in the thread, illegals used to enter the UK in the back of vehicle. However, they now enter by boat as there are no checks at either end like the channel tunnel. How much of the increase in boat arrivals is offset by reduced numbers in the back of vehicles?
Also, as pointed out by others, wars in the Middle East has resulted in millions moving westwards into the EU starting in 2011 due to the Syrian civil war (source statista Nov 2024), nine years before the UK left the EU.
Russia-Ukraine war which started in 2022 has also contributed to more people moving westward into the EU.
In 2020, migration into the EU from outside the EU was 2 million. In 2021, migration into the EU was 2.4 million. In 2022, the figure more than doubled to 5.1 million. Source Eurostat 2024.
So, as more people migrate into the EU, the more that are likely to end up in Calais to cross the channel. Remember that the ones in Calais don’t apply for asylum in France. Hence France don’t have to deal with them.
If being in the EU makes border control more effective, what difference would geography make? None is the answer.