The economy still has room to grow.
The answer is that the unemployment rate is based on people looking for work and people working. It doesn’t take into account the number of people that have given up looking for work, and that number is higher than before the most recent financial crisis.
And the reason why wages are not going up, as they used to do when employment was near full, it’s because the quality of jobs is not what it used to be. The gu’ig economy (ie. Uber driving) makes people less than minimum wage, and employers still fire at will when employees ask for higher wages.
So the picture is not as rosy as it appears and the job market has a lot more growing it can do.
Source: The US unemployment rate is at a 48-year low—so why are so many Americans still out of work? — Quartz