Answer: Because they don't have the skill to do anything so it could be anyone who wants a job!!
Explanation: If you replace a skilled worker then you loosed a skilled worker and have to search around for someone with the same or with greater skills in that specific category. if you replace an unskilled worker it's just as easy as getting that unskilled worker itself, therefore all it takes is someone wanting a job and there are lots of people without them so it would probably be pretty easy if you ask me.
feel free to copy my answer in your own words if it's useful!!
thankyou for asking hope this was helpful :)-hailey