USA spent $52.6 B on intelligence gathering

That figure is for this year alone.
How much of that figure goes into surveillance of Muslim immigrants, I wonder.
What I can't understand for the life of me is why the West  does  not either put a complete halt to immigration of Muslims or at least reduce the numbers drastically instead of letting their own countries go into bankruptcy  by spending such huge amounts of money to gather intelligence on the immigrants they have imported but are now suspicious that these same people might have terrorist links or are jihadis themselves? Isn't it better to cut off the snake's head, instead of nipping at its tail?

Here's something else to chew on:  Do you think the various surveillance organizations and corporations will ever want Muslim immigration to be curbed by even 1%?  If immigration of Muslims is either halted or cut, wouldn't it mean the end of their own spying careers and the end of such companies?