One reason is that political threads tend to bring opinion clashes, and all sort of "not nice" comments, which we try to avoid. There may be some other reasons. The ranch is just not the place for that kind of discussion.
There's nothing wrong with politics per se, provided it stays within the realm of "Be Nice". But sometimes moderators may feel that there are other considerations that make it appear desirable that some thread not continue. That may have been the case here.