As I see it, the migrants are mystified by the barriers to crossing into England, because they have encountered no resistance whatever in their travels across mainland Europe.
And why would they? They are merely transiting through, and none of these countries, including France, are their final destination, so it is in the interests of any nation to simply wave them through, with some facilities at Calais to avoid a bottleneck, and stop the migrants from getting upset from lack of support and (heaven forbid!) venturing back into mainland Europe to find somewhere to live.
It will be interesting to see what happens next.
The problem is, the genie is out of the bottle, and no matter how much the UK government try to say that there is no room or support for migrants (although they act as if there is plenty of both!) - the migrants continue to regard the UK as their Shangrila, and will continue to aim to get here by any means possible.