The same thing happened to my maternal grandfather's family around the same time frame. They moved from Somerset to Tolworth in Surrey. My grandfather was 'a bit of a lad' and my first thought was that either he or someone else in the family had disgraced the family in some way, causing them to move away. The truth, which I eventually found after talking to a more senior cousin, was that the family moved in the hope of more prosperity - a huge new dairy had just opened in Tolworth, and the family moved there in the hope of getting better paid jobs. Try researching the area of Essex that your ancestors moved to, and see if there was a new industry opening in the area which would have had a similar attraction.