There's nothing silly about building your own. What's silly is declaring a convenient, user-friendly product to be pointless because it's possible for a skilled person with a lot of free time to build their own.

If you want to build your own Dropbox with rsync, go wild, have fun, we'd all love to see what you come up with. But I don't have time for that. My family doesn't have the skills for that. Dropbox is great for us, and building our own is not a realistic alternative.