I've participated in signature campaigns before but quit when the people running them started requiring that I sign up for their websites to claim the Bitcoin. I'd rather make this as straightforward as possible -- I rent out my sig space and you send Bitcoin to an address I specify. Any takers?
Your opinion is biased because there are many campaign without this requirement. I don't know how many campaign did you checked.
In fact from my what I can see more like 80% or campaigns have straightforward payment directly to your bitcoin wallet.
I see some post like yours from time to time but I never sew anyone picked up for signature campaign after this kind of advertising.