In the twice yearly report on numbers of posts, post counts, threads that note how many posts some members have made, (which comprises an incredible volume of work kindly written, researched and assembled these days, by
@chown33, and - prior to that, by
@Doctor Q) - very often, a pie chart of post numbers is also included.
This measures the percentages of members that have fallen into each category of post numbers.
The vast majority of these - off hand, I don't recall the exact, or precise, statistic - are MR members who have made one post, or, have made between one and five posts, and this category comprises an enormous percentage of all members of MR.
A great many members (I was one such) initially join MR simply because they have a question about Apple, or an Apple product, and this seems like a good place where an answer might be found.
Certainly, this was why I joined initially; I had just bought an Apple MBP - a classic "switcher" and I had questions, as Apple differed quite a bit from the Windows world I was more familiar with.
Once their question has been answered, many of them see no further reason to remain.
Personally, I would not care much for such a threshold (number of posts) to be put in place, as it would serve to discourage those who originally join the forum - in good faith - because they merely wish to find help, or information, or an answer to a query about an Apple product; after all, the forum exists to facilitate discussion on Apple, and Apple products, and is home to a great many enthusiasts and experts, many of whom are quite generous with their knowledge and expertise.
Anyway, I would not favor anything that would serve to discourage newcomers from joining the forum - or that would serve to make it more difficult to join - who simply wish to ask a question, or seek some clarification, or information on Apple and its products.