That democrat billboard is one you make when you think you're gonna lose and you need to be able to blame someone. It can't just come out of the blue, so you make a billboard like that.
Like more than half the country doesn't vote, but you decide to focus on the three people who vote for Jill Stein who might be persuaded to vote for Kamala?
Fun how you can see the Hillary staffers effect

Edit: What are the odds that campaign will backfire because it will make more people look up Jill Stein and decide to vote for her? Like it's giving her more attention than she could have bought herself