That's all true to a significant degree. Of course, the reverse expectation was that you'd be a "company man" and spend your career (or at least a decade or two) at the company.
A lot of jobs also shifted to smaller companies in areas like tech and employees wanted to take advantage of higher salaries being offered by those firms.
I'm not sure it's a simple case of employers suddenly locking employees in. There were a lot of market forces that made staying at the same single employee forever less attractive from a salary perspective. Sort of a re-enforcing cycle. I'm sure economists have more data.
Who exactly was sending these blue collar jobs overseas if it was not the employers?
The flip side of the coin is that it's frustrating as a dev: nobody knows anything, when the entire employee base flips so often. Middle managers just don't get it, AFAICT.