1. Retailers in the UK don't sell as much gear as the ones in the US, hence to make a living they have to mark up their products.
2. You're comparing US online prices to UK retail/online prices - In the US the brick and mortar stores have bigger mark up on the products since they have it in stock, as opposed to many online stores there which only keep part of the inventory in house and the rest is being dropshipped by suppliers. UK stores use their website as an additional means of generating sales but still have the same costs as brick & mortars store do, since they have to stock as much product as possible.
3. Costs of shipping from the US affect everyone, whether they are a private person buying things in the US or a dealer ordering products in bulk - My latest order with a supplier came with shipping costs of about 6 dollars per item, multiply that by a couple hundred or thousand and you'll see some numbers that will make you say ****!
4. Last but not least, all products legally imported to the EU carry a VAT charge, in the case of UK it's 17,5%. In Poland where I reside and do business it's 22% - All VAT & Excise on imports needs to be paid before the product is released from Customs. This is reflected in the sale price.
5. Life's not fair, but nobody said it should be.