Exactly, with this relatively low support for extradition it would be surprising to see a jury conviction. And that's with abuse of the jury selection process, presumably in both directions.
I think it's a little silly to extrapolate from a general opinion poll to a trial result. An honest poll on this subject would result in about 99% "I don't know much of anything about him", and jury selection is intended to find people without a set opinion already.
Quick search for numbers show:
"53% of Americans say Julian Assange should be extradited to America"
https://today.yougov.com/topics/politics/articles-reports/20...