It's also very much about timing. If you happen to write a popular answer at the time when interest in some particular tech is high for whatever reason, that gets a lot of views and upvotes early on. And once it has those upvotes, people looking for related answers later are more likely to stumble onto it.

I still get a steady rep trickle from a generic answer about WinRT back when Win8 was the hot new thing (or mess, depending on your outlook): https://stackoverflow.com/questions/7416826/how-does-windows... - but most upvotes there are from back when it was posted, and I doubt it would get anywhere as many if that answer was written today.

And sometimes, it's the tongue-in-cheek answers that score massive upvotes, like the famous one about using regex to parse HTML.