Long threads don't work for the same reason they've never worked on this type of message board.
1. The zig-zagging back and forth left and right across the page.
2. The difficulty in working out who is responding to which post, often you can to manually trace back and look at all the posting dates and times to try and work it out. On a more modern forum style it's easy to work it out with "reply and quote" functions.
That has remained unchanged by the recent alteration.
It also doesn't mean I'm demanding a new forum, or forcing it on people, or any other such nonsensical hyperbole.