Another change since then was the rise of the corporate raider. Used to be that you could run a public company without profit as the primary motive. Parable of the Mexican fisherman, and such. (https://bemorewithless.com/the-story-of-the-mexican-fisherma...) But now people like Carl Icahn (and Mitt Romney in his private sector days) actually hunt for companies that are not maximizing return to investors, and remake them into companies that do. Apple actually had to fend off Carl Icahn recently. (http://www.marketwatch.com/story/carl-icahns-2-billion-apple...)
You need fewer janitors now because modern chemicals allow cleaning same space quicker (and probably tools also changed a bit, while maybe in the U.S. in 1980s, modern ones have already been in place).
You need more engineers. And they impact work more because development and marketing (which also became a branch of engineering, see: growth hackers) is more important now than production.
You can always train enough janitors, not so easy with engineers.
Same thing about nearly all low-skilled workers. They are easy to train and their supply is nearly infinite, demand isn't, and demand for high-skilled is high plus they make so much profit you can actually afford paying them a ton of money, which wasn't possible back in 1980s.
It is that proverbial bifurcation of workforce. Outsourcing has nothing to do with it. It is just technological change. There is no way out of it (at least no way which won't cripple economic growth - which is already not so good).
To give one example that goes back a little further, companies used to handle the whole payroll process themselves. Now they use ADP or whoever.
There's also been a lot of automation/self-service of mundane tasks. You don't really have the stereotypical "starting the mailroom" job any longer nor do you have the steno pool.