Each rank have limitations while wearing a signature (links, colors, style etc.). A newbie signature can only contain a limited amount of characters and impossible to make it colorful which makes his signature less visible compared to others and what the campaign owners want is to advertise their services and since It's not visible = worthless.
Besides what MadGamer said, think about it:
If campaigns accepted newbie members, wouldn't it be easy to abuse the system and just create like 20+ newbie accounts or more so you can earn with each account? It's not rocket science. Signature and image restrictions are there for a couple of reasons.
Hello guys,happy to be here. Could you give me your knowledge about the reason why newbie like me is not allow in the campaign.
Because before you will participate in your first Bounty - you should understand the basics of cryptoworld. You need some time for it.
And nobody is interested in 10+ newbie accounts from just 1 person.
Thank you all Guys, the answers satisfied me very well. You really deserves your rank base on the quality of your post. I salute you all.