Initially it was protected. Mostly because of off-topic answers being left. But protecting doesn't, and didn't prevent it getting comments. The only way to prevent comments is to lock the post down completely.
And I can tell you - It was getting a lot of comments. Not just on that question but on the answers too. This isn't a discussion forum, it's a Q&A site. It's not the place for extended discussions.
Moderator comments were left on the answers reminding people not to get into extended discussions, but that was to no avail. Comments still flooded in, many got individually flagged as off-topic, argumentative / not constructive. It was proving too difficult to manuyally intervene and determine each comments worth, when it just led to more comments flooding in.
There were over 80 comments on the question and accepted answer alone. That isn't manageable or sustainable. Nobody would be expected to read through all those comments. If they were important enough to be relevant to the question then they should be left as separate answers.
The focus should be on answering questions, not discussing the question or the answers.
For that reason I locked the post. It has plenty of votes, an accepted answer and 17 other answers too. Way more that the majority of questions on this site do. It's no longer a useful post, its about 90% noise (and that's with the comments removed). It's locked down now to try to preserve what useful content there is in there without it descending into long arguments about why CLIs are / aren't useful.