Well I am not sure it was purposeful, I don't know. The nefarious reasons would be what you are suggesting. In Canada it was for cheap labor and folks who will work for minimum wage. I would suspect it's for those reasons if I had to guess. Immigration (legal) is a huge net positive for the economy in almost every economy. All the measurements and research generally agree on this.
Obviously illegal or under the table shit is unquantifiable.
I hear that.
But recall - when it got to the point where the mainstream couldn't hide it, and they got pressed, the answer became they needed a "bipartisan border bill" to close it, but Trump, although not in office, had it blocked.
But it was blocked because it also contained billions for Ukraine (i am all for single item bills) and it also normalized crossings of just under 5k a day, or 1.8M per year.
But Trump closed the border without a bill so that proved all of that leftist gaslighting to be false.
AND, Biden canned the Stay in Mexico policy that Trump enacted. So that implies it was intentional, unless he was only doing it out of spite and to appeal to the base, but that helped with the surge.
So, until I hear a real good answer, I have to go with the congressional seats theory, since the math works.