Bringing back campaigns for at least J. Members, even in a limited or carefully monitored way, could motivate more newcomers to stay, learn, and improve. While they’re getting motivated, they’ll also be building the habits and skills that could make them Legendary one day.
Well, like others I also believe that it's not worth it to accept Jr Members into signature campaigns and that's why managers don't accept them. The reason is simple, the signature campaigns on this forum are basically advertisements funded by the platforms, and the managers want high signature space to advertise a platform properly and that's why they pay more money to Hero/Legendary members than to Sr or Full members.
However, one should also keep in mind that being a Legendary member isn't enough to get in those signature campaigns. There're few or many Legendary members who're not in signature campaigns, and they don't even get any offers either but at the same time there are many members of low rank like Sr members or Hero members who're in campaigns.
I suggest you to be active on the forum and learn as much as possible by reading posts of reputed members of the forum, and when you've really good stuff that you want to post then do that without any thinking, but you must read the rules of the forum to be on safe side. Overtime, you'll start getting merits and that'll help you to rank up. Instead of creating threads like this you may focus on learning and contributing.