Yeah, that's pretty much it, and it's not just tech companies. Prior to about 1990 or so, if you spent less than about five years at a company before moving on

Yeah, that's pretty much it, and it's not just tech companies. Prior to about 1990 or so, if you spent less than about five years at a company before moving on it was considered a black mark on your resume. If it was a regular pattern you were only going to get hired if your prospective employer couldn't find someone else. So companies had some confidence they would get a return on their training investment. They couldn't force you to stay, but they knew you realized it was in your best interest to stick around for awhile. That all changed. These days, particularly in tech, it's pretty normal for people to move on after 18 months or so. While it might make sense for the industry to train people, for an individual company it's stupid to put effort into an employee's career development only to have him move on to a competitor.