I have spent 6+In 6+ years working with SE communities, and I have participated in countless examples where a surprising "third option" turned out to be the best solution of all.
You don't get that with a poll.
A poll typically starts: "Should we do {X}, yes or no?" — and users feel compelled to vote rather than voicing a "convincing argument" one way or the other. I cannot count how many times we've been asked to take some action because "five people voted for it in meta" (the votingvoting is usuallyoften that low) and ultimately nothing gets done.
It is a lost opportunity to engage with the community.
Meta is about conversation. Like I said above, it is not difficult to infer what the community wants from the conversation while allowing for the possible that there is an issue we have not considered. Polling does not do that. There is little upside to taking a poll rather than allow folks to speak for themselves. Polling should not be The Go-To Way to solicit feedback from a community. It is a missed opportunity for folks to actually participate.