I'm sure I read in the economist that the number of people doing office work has been falling for some time.
Then all that excess money from 'decent' jobs goes towards more goods and services that otherwise wouldn't be possible. I mean, people casually blow $300+ on a robot vacuum cleaner or $600+ on a phone. And now you have more jobs in industries no one predicted possible 30 years ago and so on.
Not to mention, generally, the more competitive the industry the most staffing it needs. I'm sure there's some rule named after someone about this, but hot industries go on hiring sprees and when your economy is as innovative and wealthy as the US's that translates into a high demand for qualified candidates. That offsets a lot of job loss in dying sectors.
When talking about the headline unemployment rate, it's a good idea to view this seemingly rosy figure in the context of our current ~40 year lows in the labor force participation rate[0]. It's misleading to look at one without the other, IMO.