Stack Overflow is different from the other websites you mentioned, because it is, to some degree, timeless.

I suspect that the importance of time when posting on news sites contributes to the deterioration. Some people spend more time on the website, some people spend less. The people who spend more time get a bonus in the system.

Problem is that "spending a lot of time debating online" can correlate with some undesired traits, such as "doesn't do research", "writes without thinking", "doesn't read the whole article before commenting", etc. If these traits are turned up to eleven, of course those people get banned. But within the acceptable range, those on the bad side of the range get an advantage, and the 'Overton window' will gradually shift in their favor.