It is because this place had good civilized people from the beginning. Whenever a toxic person joined the community back then and posted, they would just get their ass handed to them by the other members. Even if that didn't happen, they would notice the vast difference in their posts and others, and begin to see how unprofessional they really are. I know this because I joined here when I was only 11, and my first posts consisted of mostly abbreviations (lol lmao XD
), weird capitalization, weird phrasing, etc. But then being here for just a year changed me completely, I learned a lot within that span of time. Whether someone called me out or not, a little common sense was all that was needed to see the vast difference in how I spoke compared to other people.
And now this community has the vast majority of your 'civilized' people the way you put it. Now ignorance really cannot survive for long no matter how many new members join. Ignorance begets ignorance, and vice versa.