Because the current government won't let them all come to England.
I'm not sure that is a reason.
Migrants are "working strength". Thay do everything for less money.
Migrant can be additional/subsidized work force for a country. But a country owes it citizens -this are first priority- of good/standardized living. A country should/won't take on every immigrants wanting to come -what are the track records of this- some immigrant can be desperate -some one at the bottom or feels he got nothing to lose or no self respect can do the off's- countries can accept some immigrant -well meaning immigrant-.
This is the reason why some citizens don't like immigrants because they feel the government is allotting funds to them, thus, lessening the money for its own people. But we have to understand, that who will protect these individuals other than those countries which have compassion to humanity? So for immigrants, they should behave and follow the country's protocols at all times. That is the minimum act that they can do to revert the favour given to them.