@Switch BlaydeAs Switch said, no one "owes" you a thing. You're doing this of your own volition, it's your choice to volunteer your services.
Sadly, for the vast majority, most will never offer any thanks (most won't even vote for a story they don't like), which is actually a blessing for most new authors still struggling to find their voice.
Then again, SOL readers aren't like those on most online sites. So many won't vote until they finish the story, many do, yet they won't assign a final vote until they do.
The best way of determine how successful you are, isn't the number of reads—which could easily be how many people read the first few chapters before tossing the story entirely—instead it's the actual votes, as people who do vote are already committed to the story. So, even if they give it a low vote, that's often because of you taking the story in a direction they don't approve of, but they're still communicating something with their votes.
However, their comments are often the most informative thing of all, as there, they'll specifically tell you what you are doing well, or alternative, what you're doing wrong, for them. Both of which can be invaluable, as long as you're willing to listen.
Yet, in the end it's the combination of total reads, votes (scores)—where often the changes in the weekly scores means more than the actual score does—comments (positive and critical) and, if you happen to have the books to sell, your sales.
Because, SOL readers are unusual, as opposed to purchasing a book and then reading it, SOL readers typically do the opposite, they'll read the entire story for free, and then they'll then purchase it, just to help ensure the reader continues to post more stories to SOL.
Again, the delay isn't that they don't like the story, it's to ensure you continue to write the same quality of stories.
Yet, now we have more nontraditional viewers than ever, who now seem to be voting strickly a stories Squick factor, now much the offend readers (writing about violence, sexual abuse, incest, water sports, anal play and sometimes even the sheer sexual pleasure of murdering their companions, as a part of the sex act (though thankfully, this is still a fairly rare occurrence).
So, SOL readers volunteer their praise in much the same way SOL authors do, by volunteering the praise in a variety of ways.