Suicidal empathy is why the public lacks the resolve to demand something be done, but there's more to it. Whenever you have a policy the public broadly hates and has terrible effects but faces major infernal opposition, two things are true.
First, somebody wins under that policy. Just like inflation, there are winners under an open borders policy. Most lose, but some win and win very big.
Second, those winners have great and very entrenched power. When they say "jump," the British Parliament and judiciary say "how high?" They fear those winners more than they fear the public.
Who are those winners? It is likely an alliance of short-sighted business interests that like cheap labor, socialists who know the migrants and their descendants will vote hard left, and race hustlers who make money off of grievance.