When I first joined, signature campaigns weren't really a thing.
When I joined, I didn't know signature campaigns exist.
The problem as I see it is the dynamics of the forum have shifted completely to the point where the only reason people sign up anymore is to join a campaign, or a bounty, or a second campaign or bounty (or 3rd, 4th, 5th, etc.).
I'm pretty sure there are still people who sign up without knowing about signature campaigns, but it is indeed a very small minority nowadays. It's still better than before the Merit system, at least they can't get away with only spamming.