But again, the problem is that those other jobs have qualities that make them more attractive than factory jobs. Factory jobs are often dangerous, repetitive, boring, and in unpleasant working conditions. Granted, the entry level jobs you describe also have drawbacks - they’re also not the most pleasant jobs in the world. Generally, though, they aren’t as bad as factory jobs in a lot of respects.
And there’s a lot more of those kinds of jobs in the economy than back in the day. Factory employers have to compete with jobs that offer comparable pay but better working conditions to a much greater degree than in the past.