daz - I think you're being a little unrealistic here and perhaps ignoring Easyjet's commercial needs and what their shareholders expect from airline management.
Anyone who travels regularly knows that larger transport facilities are more likely to stay open when bad weather hits. In snow, Govt sends gritting lorries to motorways first and to minor roads last. Equally one should expect a large airport like Stanstsd to be more resilient to bad weather than (for example) Cambridge.
If Easyjet were to put a note by each booking involving Southend prior to payment being made, stating explicitly that Southend is unreliable in bad weather, then a significant number of people simply would not book to fly via Southend.
Load factors / yields would suffer and Easyjet would quickly find that Southend routes were not making as much money as other potential routes. The result would be some or all planes currently based at Southend being moved to other bases.
Southend remains a small airport that needs support - occasionally we need to be a bit forgiving when small struggling airports have a relatively small blip in daily operations