They just have different beliefs and other Christians generally don't care and thus do not challenge them. Of course these are not the same kinds of people who show up to YT debate circuits because that's a very distinctive kind of person.
> what separates young earth believers from the rest of the church?
and I answered:
> Taking seriously the idea that the Bible -- and the book of Genesis in particular -- is the revealed Word of God.
The operative phrase there was "taking seriously". Many Christians profess to believe that the Bible is the revealed Word of God, but they don't really take it seriously. They play fast and loose with semantics and hermeneutics. YEC's don't. They believe that if the Bible says that the world was created in six days, then it means what it says: it happened in six 24-hour days. You crunch the numbers on the rest of the Bible's timeline and the result you get is a universe that is ~6000 years old, and so that must be the truth because God wouldn't lie. If the science says otherwise, the science must be wrong.