An accusation that often arises on the internet forums and message boards is that esoteric Orders only have correspondence courses as a way to fleece their associate members out of a monthly fee. While that may be true of some Orders, it is not true of others.
So why would a legimate Order have a correspondence course?
I will admit that money is one factor.
The fees of several correspodence courses do go to paying the officers writing the courses. Which is a good thing. Most of the time, Order and lodge officership is pro bono ordo. Yet unless the member elected (or appointed) to the office is retired or independently wealthly, quite often the good of the Order takes a backseat to their profession and other money making activities. Issuing a fee of honor to some of the more important officers ensures that they rate the business of running a lodge and Order higher than holding a yardsale.
And not all fees are absorbed by fees of honor. I have yet to draw a fee of honor from my Order work. A lot of dues are chewed up purely by the daily operating expenses of a lodge (or Order). A correspondence course eats up ink, paper, and postage; their online counterparts end up using up expensive bandwidth space. There is also officers robes (if the lodge provides them), tools, items for the Mystic Repast, and heaven forbid--rent for the lodge space.
There is also the benefit that for an Order in that a course allows them a wider public exposure than they would otherwise have. And quite often, a course forces officers to put on paper lessons that they would otherwise just keep in their heads, only expounding upon them in lodge--heaven forbid if they suddenly stepped under a bus, all that knowledge would be lost.
Yet the benefits that a lodge (and Order) recieves from having a correspodence course is nothing compared to the benefits that the associate members get from the course.
Correspondence courses (and online courses) exist because the associate members are willing to pay for them. And the fact that some people remain in these courses after the first year is a sure sign that they find something of value in them. For the most part, it is the lesson material itself that the seeker benefits from.
Yet beyond that, the seeker benefits in knowing that they are not alone. And that is really important for those of us who are studying the occult sciences. It is easy to think that you are the only one studying such material. The courses reassures us that we are not complete loons and that there are others who believe as we do.
It also allows the seeker to take part in the Orders, even if they are hundred of miles away from the closest lodge, or uncomfortable attending, or have schedule problems, or are a person who works best by themselves. Or any one of a thousand things that would make lodge attendence hard to accomplish. Even those who are completely unsuitable for membership in a lodge (the "black-balled") can still do the correspodence course.
Without the seekers, those who recieve the course and pay for it, correspondence courses would not exist. As long as it serves their needs, the courses will continue to exist.