Dopamine reward loops, good content and a reasonable UX.
If you gave a good, detailed answer with sources, you got rewarded for your effort with upvotes more than a low effort answer. This kind of appreciation motivated quality content generators to generate more content.
as usercount grew to a certain threshold, you basically got users from all sorts of domains generating quality content covering pretty much all topics
while official UX was horrible and 3rd party apps were needed, the basic system of sorting and indendation of answers allowed for long, detailed discussions which could be navigated and followed effortlessly.
Dopamine reward loops, good content and a reasonable UX.
If you gave a good, detailed answer with sources, you got rewarded for your effort with upvotes more than a low effort answer. This kind of appreciation motivated quality content generators to generate more content.
as usercount grew to a certain threshold, you basically got users from all sorts of domains generating quality content covering pretty much all topics
while official UX was horrible and 3rd party apps were needed, the basic system of sorting and indendation of answers allowed for long, detailed discussions which could be navigated and followed effortlessly.