Migrating to a place where people can contribute more to society is both a core tenet of individual liberty and one of the most positive-sum things any human being can do.
But given that you both feign concern over visa holders' working conditions [1], while at the same time advocating for policies that lead to worse working conditions [2], perhaps you just hate freedom and were never acting in good faith in the first place.
It's just the process of learning the hard way that not heeding the warnings everyone gave is painful.
Now that they're facing consequences which we warned about (and prepped for as a result) they want to ignore it thinking that the monsters under the bed will go away.
Brain drain somewhere is brain gain elsewhere.