As a mentor, there is a saying...."You can lead a horse to water, but, you cannot make him drink" I can tell you in my experience, fully 75% of the people who do not source, see it as a choice. It is not that they do not know how, they chose to not source, all the tutorials in the world are not going to change those people.
Yes, there are people who I have taught to source or at least document their sources, but there are many, many others, who just want to add people to Wikitree. By "forcing them" to do something, we may drive them off, but, at least they understand that we are committed to sources.