I've noticed that this happens sometimes.  People will start reviewing every chapter, and as the story progresses, some people just stop leaving reviews.  This isn't necessarily a bad thing, just something that happens.  I know I'm guilty of it myself, reviewing a story and then just sort of losing interest in it.
I guess I'll agree with what everyone else has been saying and that while feedback is nice it shouldn't be your main reason for writing.  I have had stories that have got a fair bit of feedback for each chapter, and while I thought it would be nice to make the story go longer for more feedback, in the end I knew where I wanted to go with it and where I wanted it to end.  If I hadn't done that, I would have been disappointed with myself and with the final result.  I still write on Not Like We Predicted.  It doesn't get much feedback, and it isn't my most popular story by any stretch, but I always feel accomplished every time I upload a new chapter just because I've been working on it for so long.  

 So I guess what I'm trying to say is don't worry about having a readership, just worry about making your writing the best you can to make yourself happy.