I have a hypothesis, that once a thread has more than N comments, a sub-comment under the top comment is more likely to stay close to the top of the page, than the same thought expressed in its own top comment. And certainly more likely to be seen than any new thread.
Or, people are just more likely to see something closer to the top, that inspires them to comment.
Therefore, the top comment in a top page thread is itself a natural comment magnet.
I don't know of an antidote to this, except that I try not to do it myself. And wary of the possibility of a pot-kettle situation here.
Display comments in random order. Then it becomes possible to add a top level comment and have it not disappear forever into the bottom of the page, forever unseen.
Alternatively, comment as quickly as possible. Ideally, be the first person to comment. Just comment your general thoughts and then fill in everything you wanted to say over a series of edits while simultaneously improving the comment's logic, grammar and spelling. This one goes all the way back to stackoverflow. It's a habit I have never been able to shake to this day because of how active I used to be on that site. Probably contributed to my account getting rate limited here.
Or, people are just more likely to see something closer to the top, that inspires them to comment.
Therefore, the top comment in a top page thread is itself a natural comment magnet.
I don't know of an antidote to this, except that I try not to do it myself. And wary of the possibility of a pot-kettle situation here.