Exactly, and one more thing: because of draconian immigration regimes, once people sneak in, they are extremely unlikely to move out until they get some sort of

Exactly, and one more thing: because of draconian immigration regimes, once people sneak in, they are extremely unlikely to move out until they get some sort of residence, which may never come. If it was easier to get in, people will come and go as needed, and you wouldn't have massive numbers of people coming and not leaving. There are many irregular immigrants that are stuck in their new countries for decades, unable to move anywhere else at all; many even die without seeing their homeland again. In all countries there are posh, elite, nice areas, and yet you don't see everybody moving into those areas until there is no standing room. There is a natural equilibrium that is effective. So overly tough immigration policies actually exacerbate the problem of illegal immigration in this way as well.