If you compare this data with any other board, you will find that by removing signature campaigns, the number of content in the forum will decrease by an estimated percentage, and 95% of accounts may stop posting.
Comparing the activity between these boards and any other board will show you the difference.
I think that your assumption is incorrect in this matter and I'll give you some examples of why it is so.
One thing to consider is the fact that before the campaigns became popular, in 2011 and 2012, people were still posting a lot. It of course increased as time went by, but saying that it all happened thanks to signature campaigns and not the growth of bitcoin presents a very one-sided view.
Maybe people aren't posting in Ivory Tower because there aren't many interesting topics there. Maybe the best topics pop up in other sections and there's not much really left to put in there? It's a newer part of the forum established just a few years back, so maybe it simply wasn't necessary, maybe it was an experiment that did not work.
There's a thread that continues to be very active despite signatures not being displayed (Wall observer), so saying that Ivory Tower isn't active because there are no signatures there is again, not showing the full picture.