Federal Judge HALTS new travel ban nationwide

[Hindsight was 2020]

Can anybody explain to a layman like me why American law (equal protection clause) would apply to foreigners?

In the legal sense there was a court case Yick Wonvs Hopkins that said once an immigrant comes here he is protected under the equal protection laws due to the inhuman way immigrants (Chinese in particular) were treated. In a greater sense many feel (including me) our founders rebel and later founded this country on enlightenment ideals with "the universal rights of man" at the center