Because in my own opinion much better if we should learn first here before joining. Since we are newbies our knowledge is not enough to make a quality post. This is just my opinion.
What can you say about this?
You are right, learn the system of the forum first before joining to a campaign but Im not saying that you wait until you become a Jr. Member its up to you if you think that you are already understand the rule's and the system of this community you can join any campaign that fits your rank.
I read the other post from newbies asking about how to join a campaign, can newbie join a campaign and is there a campaign for newbie.
Yes there are bounty campaign's accepting newbie, you can join Social media campaigns and others, try to explore after you learn what you needed.
Goodluck bro.