> But nobody agreed to allow illegal immigrants to come and stay here.

In 90% of cases somebody did. Somebody at the border talked to them. Somebody checked their passport or their documentation (at the border). So many "undocumented immigrants" are people who overstayed their visas, like Elon did.

They literally were documented but then they didn't keep up with the paperwork and thus became undocumented.

"Doccumented" status *is* literally just a case of keeping up with the paperwork.

Some people do sneak in but the *vast majority* come through legal ports of entry