The need for steem? Well, the steem network cannot create and issue any other currency so it's either steem or nothing. If you try to print your own US dollars, you go to jail.
The creators don't actually get paid by the viewers. They get paid by the steem network as new steem are created. The value of steem comes from people that want to buy it from other people (supply and demand). Getting paid for something doesn't enhance its quality. Actually, it can have the exact opposite effect because people with nothing to say want to get paid too so they just post garbage in hopes that some sucker will upvote it. A lso, a steem that's worth 50 cents won't seem very valueble to us in the first world, but dirt-poor people in the third world will value it much more and so will be willing to spend more of their time and energy trying to spam and scam their way to acquiring it. This is why curation is so important and why it shouldn't be taken lightly.