1) Understand that outsourcing this way is an important skill and start training for it.
2) Teach subjects that are so damn engaging that students actually want to learn them.
Delegation is a good skill for a manager, but you don't go to a technical university to learn skills like this. You can pick it up in real life. (Also, it's most certainly unethical to delegate something and take complete credit -- and that's what the essay mills are supporting.)
On the second point, the subjects already are engaging, it's just that people pick the wrong topics. If you think data structures are boring, don't get a computer science degree. If blood makes you ill, don't become a surgeon. If you think the law is boring, don't become a lawyer. Pick something that you enjoy, not something that you think will be "in demand" after you graduate. Predicting the future is not easy. Pick something you like instead.
2) You can't engage a student whose sole objective in life is the pursuit of money. Many, many students see universities as a path to greater income, nothing more. They have no interest in the subjects at hand.
Take home assignments are usually a mess - what I did was to force people to write tests. If there are 3 people in a group and only one is working - it will also come out.