Mostly people want it to join the signature and bounty campaign. One part wants it to create trust for others in currency exchanges(In this case I think feedback is of more importance.)
Indeed most newcomers that come to this forum want to rank up for that purpose although there's no much campaign which accepts jr members. In regards to currency exchange with the others I think having jr member or higher rank doesn't immediately increase the people trust on you and as you said before feedback is the most important in this case, it's worthless if you have lots of negative feedback even though you are in a high rank.
However begging for merits is the wrong way to rank up no matter whats the reason behind it.
This is a notable factor. But i actually noticed that newbies and jr members spams the forum the most. And this is because they want to increase in rank so they can have higher chance of signing signatures. I think enlightening them is the best giving and deleting a spam message and sending a warning message to spammers but giving them negative trust won't help them.