Don't Easyjet have ILS on their 737's ?
All easyJet's 737s are capable of flying down to Cat. 3b limits. ABZ's ILS is as far as I know, only Cat. 1
If the RVR is below easyJet's Cat. 1 minima, then the flight crew cannot commence an approach and descend below a height of 1500 feet with subsequently, getting the ground or runway in sight.
Diversion fuel may also have been a factor.