Because the "it'll create X jobs" implies it's ongoing. It's a disingenuous attempt to oversell the benefits because they know if they're transparent about it, suddenly it doesn't seem like such a great deal.

Actually if they were honest they'd say "It'll create x careers", which is a much better deal than just a job. Friend went from 17 an hour at his first DC to 100/hr last year with 70 people on his team.