That is not the problem actually, this is a bit of a feature discussion.
As it stands the poll plugin is bundled, together with lazyYT discourse/plugins at main · discourse/discourse · GitHub
Prior to Docker days this was the only clean way to ensure adoption. These days we have a simpler story, but its hard to make a change cause we can not reach in to all the container definitions out there and include extra repos.
So for now you get latest poll by updating Discourse 