The problem is they're trying to have their cake and eat it.
They're trying to signal to the voting public that immigrants are welcome, and anyone who wants to can come in, while at the same time understanding that they're still just a burden and the country is currently being fucked to hell by the pandemic. So they roll out a welcome mat and then chase down and lock up anyone stupid enough to take them up on the offer, because ICE is apparently still being given free reign by Biden to do exactly the same things they did under Trump, just with extra ass-covering on Joe's part.
Which is why these migrant detention centers are now 700% beyond capacity and conditions are even worse than they were under Trump, because Trump at least was willing to nut up and say he didn't actually want illegal immigrants, instead of talking out of both sides of his mouth and compounding the misery. Right now these people think they can just hop across the border any time they want and they have it made, because that's the lie the Democrats are selling to the public, only to then promptly get the shaft.
It's more sadistic than anything they accused Trump of, and it's all rooted in their cowardice and greed, rather than merely cruelty.