Gatwick's CEO says that 10,000 passengers were disrupted last night - so excluding the huge disruption of passengers this morning. That was 2,000 passengers unable to fly out of Gatwick, 6,000 passengers up in the air who were redirected to other airports, and 2,000 passengers who were unable to leave a country inbound for the UK. Plus all the friends and relatives waiting at Gatwick to meet passengers who landed in a different part of the UK.
As someone who frequently does long-haul flights, the last thing you need is a major disruption.
And then there's the cost, which is huge, as Thousandyard has just said above.