Perhaps EZY were happy to set up a SEN base with a 17 hour operational day, while the Council were also able to placate the noise lobby by reducing greatly the number of night movements allowed from 900 to 120 per month. That small number would not have given much scope for night scheduled pax operations in any event. In the '80s and '90s SEN supported a fairly intensive night freight operation that included types such as Carvair, Viscount, Herald, Electra, CV-580 etc., none of which were particularly quiet, so I doubt if it came as much of a surprise that the B737 later found itself in the role of freighter operations.