Why would billions of people come here, because trying to make a new life as a blue collar worker among them millions of citizens who hate them for even trying is intrinsically such a great deal?
The state of Florida has a nice chart of how many gang-affiliated undocumented immigrants ICE there has picked up ("Demographics" tab, bottom right), it's under 0.5%:
The gangs-and-crime angle was necessary to sell the concept to a number of low-information voters, but that was never the plan.
Pursuing gang members and actual criminals takes work and effort. Snatching random Hispanic people from their construction or dish washing job without consideration to gang affiliation, citizenship status, or much of anything else is much easier, within the capabilities of the psychos the Trump administration has granted license to the agency to hire straight out of the local outlaw biker bar and/or gutter for the job.