All my business are shutting down and being abandoned due to "unskilled workers" I have a maxed out gradeschool, highschool, and a university with 3 dorms and a science wing....complete bustop coverage for the city...and the max amount of buses...wtf
I'm not sure, I had the same issue more times, then I figured out it was just a matter of having people in the city and the ones I had were not enough, despite the industries' message was not very clear.
Also, this happens when you put high density roads around the industrial areas. So when you do that, do slowly or make the city be crowded first.
To do that, just lower the private's (citizens only) taxes to 7% or less, they'll come in and will let your city double, so your industry will keep up (that you then must tax for about 10% or you'll not be able to earn money).