The name of one of the factors is "selection bias". The type of people willing to take the survey may be those that already feel strongly on the topic, meaning

The name of one of the factors is "selection bias". The type of people willing to take the survey may be those that already feel strongly on the topic, meaning you get results that favor one or both extremes, with fewer in the middle. Or the survey delivery mechanism makes response from some population segments less likely: Results collected purely online may not get as maney older people less comfortable with technology (although that's a dwindling group). Results collected through email solicitation may not get as many younger respondents who don't use email as much. A phone survey sent out during the day will miss many people who aren't home, which will skew the results by excluding many people who are already comfortable going out, shopping, back to work, etc and move results towards "permanent lockdown".