Integration with google services,better friend management,better mobile app,easier to find stuff to share,you can get your data back,better photo tagging,strong group chat features,safer content sharing,google is a better steward of your personal data.
I don't think the "Facebook started first" argument holds water. Anyone remember Myspace? Yahoo Groups? I predict G+ will outstrip FB in the future. It has the backing of webmasters and, most importantly, the backing of Google itself. I would imagine they have hundreds of people working night and day and endeavoring to improve their market share and, eventually, dominate. What stops them leaping to the head of the class right now is indeed the FB started first factor. Social networks are hard to grow because, by their very nature, they require other people using them in order for you to - wait for it - network. So that alone makes it a slow process. Then you have the demographic that can't understand G+ usage or is simply unconcerned about learning a new platform (likely the 60 / 70+ demographic). So to outstrip FB, Google need to make G+ more user-friendly, and continue to incorporate elements that make it fun, useful, and perhaps even necessary. This and a lot more, I would imagine they're already hard at work on!
Seems to be growing fast in stats put out by google (for share holders), but reality is they are just pushing google and gmail users to click on google+ button. Then no one actually hangs out or puts content into it. You look at google+ profiles and most of them are just empty. Google also plains to scrap all user info and run it in ads with real names last name included attached to the ads. This will not go over very well with most people. Come hang out with friends and family while we scrap your info and publish it for profit ? No Thanks. Its hard to say who will be the next social network king but I don't think it will be google+. The layout is not that great and it is to aggressive with the personal info scrapping.
Google + looked promising, but it's their design that i think needs improving. They could make finding friends easier and creating easier connectivity dashboards always helps when it comes to social networks.
I think that Google+ is owned by Google so that Google+ will help you get higher rank when using Google search. It's my own opinion, I am not sure it's true.