Why does everyone think that the average person agrees with them? Because most people talk to mostly their friends, family, and co-workers, so they often experience a bubble of similar ideas, and psychologically make them believe their opinions are more popular.
Polls are generally not a reliable source. I'm not going to list every issue that polls have right now, but some top issues include inadequate and unrepresentative sample sizes that lead to large margins of error, publications not knowing how to reach a specific audience or demographic (this is cited as one of the reasons why polls predicting the 2016 presidential election were way off the mark), polls that are only or mostly answered by people that have a major stake in an issue (or a vocal minority), polls that have vague or generalized questions that do a bad job at gauging the proper feelings or opinions on a topic, questions that are phrased in a way that leads the user to answer in a specific way, either maliciously or unintentionally, or sometimes polls that are edited or shifted in a way to push whatever agenda to publication is trying to push, you know, bias. At best, polls could be used as a pointer for a direction to look at, or something to consider about how a community feels about a subject, but at no point should they be used as gospel or as proof that a certain community believes in something, thinks a certain way, or has preference for one project over an other.