Put simply the number of jobs available is less that the number of people unemployed.
To complicate it you need to match a persons skills, experience and attributes to the job. Then there is the location of the jobs, it's not always easy or possible to relocate to the location of the job.
At any given time there are jobs being created and jobs being lost, in some case we have seen huge demand for particular trades that to fill a vacancy just creates another vacancy.
It's never so simple and if we ever got to the situation that there was a job for every one we would have the situation that people would not do certain jobs.
We had similar situation pre GFC when small business where putting up signs on shop window wanting staff, when they got staff they would not last long as the would switch to better jobs.
Yeah life can be simple on the individual basis but in the bigger scheme of things it can be a lot more complex
