There are 7.8 billion people in the world. Obviously, many surveys are only intended for a certain audience, and even in very general surveys there is a problem of getting that many people to take part. But the more people you ask, the more likely you are to get a general result that really reflects the average or majority answer.

Say you are friends with a lot of model train enthusiasts. You ask the first 30 people you know for their main hobby, and the answer will be appear to be overwhelmingly model trains. But expand that to the first 300 people you know, and some more common hobbies will end up being the result, but model trains might still stick out as being quite a popular answer. Expand that to 3000 people, and you'd start to see that model trains are actually a pretty niche hobby.

There can still be biased or unusual results in a survey with more people, because you have to consider how the participants were found and how diverse they are in other categories (for example, a poll on Reddit with thousands of answers will still only reflect the opinions of people who spend time on Reddit). And a smaller survey could actually have very representative answers, but this is hard to know.

There's a lot to consider in statistics. But it's generally an important factor to consider to get a wider distribution of answers.