Whereas the assembly-line worker of years past could be trained in days and replaced at will, software engineers working on large codebases can take months to get up to speed on a new team. Unlike the replaceable assembly-line worker, these people need nurturing, time, and space to think and create.
A key part of this equation is employee mobility. If the employee doesn't like their manager/company, they are much more likely than their blue-collar or historic counterparts to be able to find a new, great job.
