Because if it just said 'people', someone else would ask, "are they allowing _anyone_ from _any country_ to join, or residents, or citizens?" You're assuming t

Because if it just said 'people', someone else would ask, "are they allowing _anyone_ from _any country_ to join, or residents, or citizens?" You're assuming that the wording of 'people' should be obvious, and other people will find it non-obvious. They just picked one.