I think that the linked article speaks well for a large number of cavers of similar experience levels. I've been through most of those phases myself.
I find it interesting that this question is seemingly asked by cavers to one another than it is by non-cavers. Club publications and online forums are full of similar discussions, and have been for decades. I think we're really asking ourselves what the point is. We keep asking, and keep giving the same answers, but I don't think we're very satisfied with those answers. Similar to Chunky, above, I don't think many cavers can get at the real answer with words, but we agree that caving fills a need.
What need?
Selfish needs of the ego, partly. Caving is often competition, expressed both in the lust for virgin passage and in the unrelenting public display of our exploits. A need for excitement? As stimulated by the thrills of the uncommon landscape and illusion of danger, the excitement of caving wears off quickly, and must be replaced by something more substantial. As common as these motivations to cave are (they have impacted me powerfully in the past), I believe that something else, and more honorable, may be among the roots of caving's attraction.
Caving forces us to focus our attention on an extremely small natural place. In a time when we increasingly place ourselves above our natural sources, and in an industrial world whose most powerful doctrines demand contempt for small places, when caving we find ourselves within and beneath our natural sources, seeing even small nuances of small places and finding that they are interesting, beautiful, mysterious, and consequential. I believe that the most real and healthy need that caving can fill is the need to be an intimate and knowing partner with the natural world. This is a biological, emotional, and spiritual need that is difficult to meet in a commercial world of forcible divorce.
In my own case, after the superficial thrills of danger and discovery were gone, I found that I still loved caves and caving. Then I recognized an immense hypocrisy among the "caving community" including myself. Cavers often attach huge significance to cave animals, cave morphology, news items involving caves, cave geology, sediments, minerals, etc. etc., while having relatively little knowledge of or apparent interest in the natural world outside the cave. Again, the nature of the cave forces focus, and the objects, focused on, are found to be good. The lesson too often unlearned is that the whole of the natural world is equally as fascinating as caves are. I had to be taught this lesson by farmers who (involved intimately as a few of them still are with the natural workings of soil, fertility, growth, health, and decay) carry an astounding body of knowledge with an equally significant respect and love for their work.
If cavers never recognize the gift they are getting from their small but deeply personal involvement with natural places, they will be destructive of those places. Much evidence suggests that cavers are missing the biggest point that caving can make, and are either ignorant of or unappreciative of the value of earth as a whole. The moment that cavers do recognize the real value of the cave, they will see a correspondency with the earth as a whole, will become more nurturing and reverential of it, more interested in it, more blessed by it.