Which is one way to ensure not too many people sign up. Losing people that you expect to lose in a couple years saves some money and presumably everybody was planning on them retiring soon anyway and so had plans in place so knowledge isn't lost.

It might also get a few people who have personal reasons to leave, but headcount is lost with people who wouldn't stay so there is no loss.

Boeing has done this voluntary offer several times. The goal is specifically to entice people who have 25+ years of service and are at or close to eligibility for collecting their pension.

When I worked there I had coworkers who were ready to retire but were hoping for one of these rounds so that they could get a little extra on the way out.