The UK is an island but our borders have more holes than a colander. Illegal immigration and people smuggling are a huge issue here, and a political hot potato. The problem must be 10x worse for countries with land borders.
A few thousand unorganised migrant workers who are trying to smuggle themselves in with no more than a suitcase each and try to hide in the corners of soceity when they get there is quite different from a massive uniformed army with tanks and trucks who then try to take over the running of the government when they get here.
Also the army was legally allowed and ordered to shoot the Germans who were trying to come over, whereas they is not the political will to shoot migrant workers.