It's actually a recruitment agency issue, and not a government one. Agencies use sites like this to increase the numbers of candidates available to work.

I advertise for jobs myself, and they have made it so each vacancy you register with them is supposed to be for a definite role, and they issue job numbers, so this can be audited at any time.

I would imagine it is the industrial agencies that do this, as they will need lots of unskilled workers, but not necessarily all at the same time, so they keep vacancies running, even though they may not have specific jobs available.