Following type of users are posting here without the need to get paid
1) There are users coming through google search based on any crypto related problem they are facing and for which a thread has been opened here. They will share their experience also in the same thread. Since, this forum ranks very high in search engines, this constitutes a good percentage of overall members here.
There could be many reasons why a someone could get determined that they wanted to join this forum, some could be through their search on the internet, while some may be by their friends referrals, but the truth is, this is bitcointalk where we make discussions about bitcoin and get to connect with others from across the world in this discussions, posting to get paid will now determined by whom you're posting for, or who hired you or not for doing that, but on a general level, everyone should post here freely and without being obligated for being paid.
2) Same way there are many members here just to improve their knowledge about crypto and to know the recent news related to crypto. That can be a bigger incentive for them than paid signature campaigns especially if they are investing big amounts in crypto.
You're right, some already have been here over time without having considerations for joining a signature campaign and they enjoy it that way because they are not after that, some may as well reconsider to participate and that's not a problem, there are criterial in joining one, but what people must understand is the fact that this place is not a money making platform, we are only doing that as part of the benefits we got served with being a member and the main purpose is for bitcoin discussion, i think there are other threads discussions as well being allowed aside that for bitcoin discussion, like politics and society, altcoins discussions and gambling.