Why is DropBox so much more popular than other similar tools?

I love DropBox and I'm intrigued by Quora so I was happy to see this post asking why DropBox is so popular compared to other file syncing solutions. 
"Well, let's take a step back and think about the sync problem and what the ideal solution for it would do:


There would be a folder.
You'd put your stuff in it.
It would sync.


They built that.

Why didn't anyone else build that?  I have no idea.

"But," you may ask, "so much more you could do!  What about task management, calendaring, customized dashboards, virtual white boarding.  More than just folders and files!"
No, shut up.  People don't use that crap.  They just want a folder.  A folder that syncs."


Exactly. DropBox does one thing very well and it doesn't try to make you do anything new. If you haven't tried it. Do. It's an amazing way to backup and sync your stuff.