Totally agree with you. Sharing is one way things get viral, but I think it is because the steemit does not really have the function like making friends in social network like FB.

Also, while counting rewards, steemit currently calculate anything happens within steemit. Because new you don't really have friends in steemit, you might only share with people maybe in FB, Twitter, etc. But sharing it with other social media would need further rules to establish rewarding system. (After all, in other media, bring your "LIKE" is free.)