I guess it's just how it's been designed for both people young and old. Younger people have an outlet for creation, where rules don't really apply and you can do just about anything, where as older people use it to reminisce over their own childhoods. It's gotten even more popular because of YouTubers doing LP's of Minecraft. Programmers have a place too, where they can not only create amazing redstone creations, but create mods, and even program in some mods. The abilities you have in just vanilla Minecraft is already pretty extensive, and if people 5 years ago saw what it's like now, they'd be enthralled. But yeah, I believe it was a matter of right place, right time, because a few years earlier or a few years later would've resulted in a smaller userbase, but it was released just at the time where teenagers who played these old games wanted to play them again, and younger people wanted something new.