Unemployment isn't a good measure of the thing we care about. Two factors for this: the politicization of the statistic, and a more fundamental mis-calibration.
The mis-calibration is that unemployment looks at how hard it is to fill job openings - basically, it's the ratio of job-seekers to filled positions. When it's higher, there's more candidates trying to interview for the average position. When it's lower, there's fewer. This is a very distinct thing from what percentage of folks are productive members of society; the 40 year old mill worker that cannot retrain to a non-obsolete role ends up being "disabled" and not an unemployed job-seeker.
The politicization is why we talk about official unemployment numbers as they are measured rather than more rough measures of labor participation. The unemployment rate is used as a measure for the effectiveness of various economic policies and political entities, so those policy-makers and political entities have decided to talk about the ones that make them look good. Goodhart's Law in action, basically.
