Like others said, it allows for syncing/cloud storage, and while you CAN use your gmail e-mail to create one, no, it doesn't sync to your Google account, it does so to One Drive (which requires a MS account, which, in turn, can be created using your GMail account... hope I didn't make that sound too complicated).
I'm not bashing Keep, mind you, just stating that it's heavily 'underpowered' in comparison. And that's not bad! It's simple but it's great at what it does, unlike other note-taking apps that want to do simplicity but end up feeling just incomplete. It seems, for you, what Keep does is more than enough, and using a more featured note app might even hinder your note-taking experience. So just go with what works, but if you're looking for an S-Note replacement like the OP wants, Keep is never going to make that list.