I know people living in shitty places that are making a living thanks to signature campaigns. High unemployment, low payrates, 3rd world standard of living. Some have enough good english to keep making good posts and make more of what they could make working some slavery job. The importance of the signature campaigns is underrated, they save lives. Someone with good english and a computer in Peru that has a Hero account can be making above average monthly income. Signature campaigns are one of the main tools to distribute Bitcoin around the world to all kinds of people.
On a grand scale, the number of people making a proper living from these campaigns is almost neglectable though.
However, you do raise a valid point, as certain people will benefit from these campaigns more so than others.