Because their servers and owners are located in countries with a different view on intellectual property rights (countries like Russia or China), where such things are tolerated if not outright legal.
You on the other hand are a British citizen (according to your profile), and under British law. Breach of intellectual property rights is a serious offence in most Western countries.
Keep in mind these webistes make money out of this, so don't trust them when they tell you this is perfectly legal "bacause you don't download anything". It's in their interest to con you into helping them boost their traffic, more traffic mean more revenue for them.
Originally posted by The_Black_Smoke:
We have only been up and running for 2 and a half months but already have nearly 500 members.
You forgot to mention 75% of those members never made a single post, sugesting they just joined to watch the episodes. Less than 10% of your members made more than 20 posts.