Upvotes and follows. Have your friends join to upvote and follow. Plus they might like what you have to say.
Rewards. Bribe them! Who doesn't like earning rewards for their post AND their comments?!
New friends. You can virtually meet people from all around the world, and learn more about different cultures and lifestyles. All in the comfort of your own home without costing you a dime to travel ((until you make enough steem, cash out, and do some world traveling.... But unless you're that good, it will take awhile!))
People truly caring. Now not everyone on here is going to like what you have to say, but at least most people care on here more than they do on facebook!
Uncensored. Nearly anything goes.... And guess what?! Unlike facebook and twitter, it's not too often you come across any high school drama!
Information. No bias search engines preventing you from learning truth in a variety of things.
These are just a few of the reasons, and I'm sure most of these are why you joined too!