1) Why is this? Is it because both sides share it vs just typical echo chamber sharing? I know it's not "shared more because more people believe it" as the US is pretty close to 50/50.
TLDR is that if you know certain subjects will get your base talking about something else that you aren't allowed to promote (such as a conspiracy theory), you promote the hell out of real news stories about those subjects knowing your base will a) share and b) discuss the conspiracy theories in the comments.
It's a very clever way to use money to boost the conversation around untrue claims, while technically neither the ad buyer nor seller are responsible since it's the users doing the lying. And I don't know what the solution is, fact checking every user comment isn't feasible..