I thought the US was somewhat unusual in its lax treatment of illegal immigration. However lying to or sneaking past border officials to enter a country is literally a crime yes (certainly for foreign nationals, and probably not kosher for citizens to do either). Though entering on a visitor visa and overstaying is just a civil violation with a civil penalty (deportation). If a citizen had a record of using false identity documents or trying to evade legally-enforced border crossings, a fair algorithm would presumably have to take that into account just as well.
Well if you enter as a legal visitor through a border checkpoint you give the govt the opportunity to do security checks, restrict import of various things, charge customs taxes. Plus they have an idea you are there. It makes sense that sidestepping some or all of that screening and record-keeping will be treated more harshly.
