All other answers defending the blocking or disabling of comments are cowardly, just like the people who block/disable comments who we are discussing. So I guess I’ve answered the question… It’s because they’re cowards, who can’t, on a logical and/or moral level, defend the content they’re uploading. If the content is fundamentally sound/righteous/correct, and the uploader is competent and not a coward, having the intellectual ability to defend said content, there is no reason to block comments. Again, they are incompetent, weak minded cowards! Any person who takes steps to avoid criticism, or suppress actual, real life prevailing beliefs or opinions (even if those beliefs/opinions are wrong), is inarguably an incompetent coward. Anything of substance, value, and truth is ALWAYS worth defending/standing up for.
If ya can’t take the heat… Stay out of the kitchen!