One of the things to remember with TT, is you should be able to use your plan for 10+ years (which is probably long enough), not necessarily "forever".
There are really two companies, one (the one you deal with) "owns" the memberships that allow you to camp. The other owns the campgrounds and gives the membership company a long term lease to allow camping. The current agreement is good for about another 15 years. So far they have just kept extending the agreement, but there is no requirement that this continue.
They set it up this way to allow the TT membership company to go bankrupt without effecting the land-holding company. Not that I'm saying this is likely, but it's their business plan to protect the land in a bankruptcy situation.