DNA evidence alone is usually not the reason jurors reach a guilty verdict. I suppose the quality of other evidence and independently supported facts presented to the jury play a role even when there is no or disputable DNA evidence.
No, but it is a big one.
Also a big player in the "No DNA, must be innocent" mindset as well.
Juries are made up of people and people do not like to be wrong. And most moral people really would hate to send someone to jail who does not deserve it.
DNA was something the juries have been told, through the media, is a slam dunk sort evidence that means you can not get it wrong. So they rely on it to a ridiculous degree.