OK some reasons perceptible to me:
1) few posts history but very opinionated contributions en masse (within a short time) along the way of controversial issues already discussed in past threads leading some forumites to query agenda or cover of other personalities (eg Max Carnage). His/her confident reference to statistical sources point to a seasoned frequenter to SS.
2) add little to previous threads on rehashed topics such as Demographia statistics, integrity and appropriateness of debt income ratios, international comparisons, revisions of views of global economic institutions eg IMF. However, one-sided usage and interpretation of statistics only reinforce spam-like purpose behind contributions
3) challenged by some forumites for any reason of continuing (in almost hysterical outbursts) but did not respond or take stock of posting style. The style was beginning to advance perceived personal agenda (pushing public psychology toward the downside so that it becomes self-fulfilling) than contributing to forum knowledge
IMHO