Why do new web designs go down like a lead balloon

When I go to a website with a new look I think ‘cool’ (unless of course it isn’t), yet it seems I’m in a minority. Even when you consider that unhappy people are more likely to complain than happy people are to compliment it still amazes me that people are so openly hostile to new websites and say things that they know will be read by those who have spent months working on it which are very uncomplimentary.

Examples:

I don’t know any other medium where people are so ready to knock down the work of others.