[sva_]

> makes me wonder why any employer would ever prefer younger employees with nothing tying them down

Probably a lot of reasons, but a major one may be that young people with no family of their own got all day, every day, to think about work-related problems - especially so, if they derive a lot of meaning from their work, as many people do. It's probably also a lot easier to boss them around, especially if said people crave acknowledgement from some authority figure.