I got this impression too, without looking at the detailed statistics. I don't know if it's because of the mixer ban, but it seems to me that the activity on the forum is significantly weaker.
They probably evaluated the results at Bestchange and may have recognized that they had reached the maximum on the forum. Looking at the history of sig campaigns here, many services ended the campaign after a short period even though they needed a slightly longer period. 4.5 years is quite long, it requires a lot of patience and of course money.
I've been on this forum for about 7 years, at the time I didn't even know there were signature campaigns going on in the forum, I joined here because here I find knowledge that i can't get on other social medias like Facebook etc. And the knowledge I was obtaining from these medias was not enough. Here are the biggest experts, there are a lot of good people here who are not just here to get money with signature campaigns.
I only heard about signature campaigns when one came up on my local board, i think i was a Full Member, it didn't pay much, but it was a great experience to understand how it works.
I believe that we can maintain our activities on the forum even if we do not participate in a paid campaign, of course everyone has their own tasks, work and sometimes there is no time to participate every day, there are days when I spend more time on this forum than on other networks social media, I spend more time reading posts than writing, I feel good here, it's a refuge from my personal problems, bitcointalk is my second home.
I hope that the trend of forum activities returns to its glory days, I hope that advertisers don't get discouraged from having their services promoted here, as this is the culture of the forum.
Of course, we shouldn't just think about getting receive money at all costs by making low quality posts, we must preserve the good practices of this forum and the signature campaigns are just the consequences of our good work.