Get Out: why do they take two drastically different approaches?

Chris discovers that he's the victim of a scheme where the family systematically lures black people to their home. Each attempt seems to span several months because it requires Rose to date the men first.

But at the beginning of the film, another victim (Andre) is simply kidnapped by force with no build-up.

Why does the family repeatedly carry out this long, painstaking scheme when kidnapping a dude off the street works just as well?