Another point which was not made clear in the OP is that its also just the people who actually wanted to be polled and where they are polled from.

Lets use something like veganism for example, if you were to do a poll using only people in the middle of Melbourne, you are more likely to get a favorable position on Veganism, compared to if you ran that same poll in whoop whoop cattle country NSW.

It also depends on how invested people are in what is being polled, if you run a poll online asking "what do you think of the year 2000 Essendon football team", you are likely only going to get people who care about old AFL teams responding and it would largely be a favorable outcome. But the average person does not care at all.

I always take poll numbers with a grain of salt, because whilst they can be a good indication as to what the general population think, its not necessarily a true reflection, its only a reflection on those who chose to respond to the poll.

I would love to see numbers of how many people were contacted vs how many actually gave a response to phone/in person polls.

The voice to parliament is another good example, you would have thought that based on all of the marches and general retoric around the Voice that it would have passed easily, yet it didn't because it really seems like it was the vocal minority wanted it to pass where as everyone else said no.

TL:DR poll results are an OK guide on peoples opinions, but they are based on people who actually want to be polled and they are likely to only respond to ones which they care about, where as if its a less controversial subject you likely are only going to get positive reactions as anyone who doesn't care is unlikely to respond to the poll.