So this is a complicated issue, and there's no way to go through all this briefly, but I'll try to give a brief summary that doesnt cover EVERYTHING driving this, as I'd have to write a fucking book here to cover it all.

The reason mass immigration from non european nations began in the US in the first place is the Hart Cellar act. The Hart Cellar act was instituted in large part by heavy Jewish lobbying. Now why would they have cared about importing large numbers of non Europeans to the US and causing this to accelerate by chain migration? Well, we know why, because some of them explicitly said why when talking to a largely Jewish audience, they said it was because Jews would be safer in a "multicultural" society. The logical reason being if you are the only minority, or one of the only ones, then you stick out like a sore thumb, and at least theoretically would be more likely to be persecuted.

Now the US at that point had never had any real history of serious persecution of Jews. Certainly no pogroms or any violence aside from a few scattered incidents. So why would these Jews think it was worth permanently altering the US demographically over a problem that hadnt really existed in the US? WW2 and their experience in it is why. Again, we know this because some of them stated it, albeit to Jewish audiences only.

Now this is a very dubious strategy, especially when you consider that not only had Americans not had a history of serious persecution of Jews, but because the country had even just fought and bled fighting a country that had persecuted Jews. Germany. So while this may have been their motivation, it was a stupid, short sighted, narcissitic and ultimately self destructive one, but so great was the fear and antipathy towards white christians resulting from ww2 of a segment of the Jewish population that they deemed it needed to be done anyway, and it was this segment that drove this pro mass immigration effort and a lot the continually escalating anti white pseudo social science that has since taken hold of the US. This certainly doesnt mean that all Jews bought or buy into it, but a very fanatical, dedicated, and well funded segment did, and a larger segment has passively gone along with it, and any suggestion that this happened has generally resulting in nearly all of them circling the wagons and attacking anyone who suggests it, despite it, you know, being true.

Obviously since that act there have been plenty of wealthy Americans who also encouraged mass immigration solely out of greed, with no real racial/ethnic motive or concerns, along with other Americans who went along with it out of a sense of bleeding heart guilt(both of which the previously mentioned group of Jews exploited heavily).

Now in Europe, in the examples I mentioned where it has been proven there is no economic benefit, by that I mean pretty much no one. I mean literally no one in Sweden benefits economically by importing massive numbers of Somalis or North Africans, not even their 1%. They have been a complete and total economic drain to all segments of society aside from maybe a tiny percentage who work in the "diversity" industry, funded by people like George Soros, who does not personally economically benefit from this but has other ulterior motives that almost certainly dont involve the wellbeing of Swedes or Europeans.

So, the reality is that this is not SOLELY economic. I havent even gone into the partisan politics of it, whereby some Democrats believe it is politically advantageous to import large numbers of new voters they think will be more likely to support them, "replacing" the ones who dont.