Not really sure how commercial caving ever became the focus of this thread but as it has let's not beat about the bush.
It should be patently obvious to anyone with a modicum of common sense why commercial caving is not allowed in OFD - i.e. if it was allowed the place would be even more trashed than it already is.
The ill-advised decision to open up Top Entrance in the first place, although possibly understandable at the time, was a major disaster so far as the long-term conservation of the underlying cave system is concerned. Everything that has been done since, including all the rules and regulations regarding access, are merely a pretty ineffectual damage limitation exercise.
As things stand, the cave is, in my opinion, vastly over-used by cavers conducting the same old tourist trips week after week, year after year. The only redeeming factor in this is that the overwhelming majority of these stick to the major trade-routes, all of which were ruined long ago so it doesn't really matter. However, not far off these trade-routes, unseen by most tourist cavers in their haste to do the trip in record time so they can make the pub, there still exist many wonderful formations. In some cases these are exceedingly delicate and are very, very vulnerable. If commercial caving were ever allowed there is no doubt that the existence of these formations would be under threat.