OK, the problem you have in the UK (but also conversely the advantage in most cases) is the Sales of Goods act 1979 (as amended).
As you probably know under the SOG your contract is between you and your retailer/dealer and NOT the manufacturer. This means that you could not go to Heliguy/Quadcopters UK etc and expect them (nor would they have a legal obligation) to put right anything that went wrong (you have no contract with them.
This leaves you with the option of going directly to DJI, which if you are UK based would now be in the Netherlands.
I would expect (providing you can show proof of purchase from the US) that a worldwide warranty should be honored.
Please note though - I have not seen this tested in the real world.
DJI EU Support is excellent as long as you have a genuine issue and can provide all of the required supporting evidence / documentation as they have to protect against cases of fraud. I've had reason to use them on three separate occasions and each time found them to be far more efficient and easy to deal with then most of the UK-based computer support companies I have to liaise with on a daily basis. Generally they want to see screenshots, logs, pictures of damage and of serial numbers, purchase invoice and, if appropriate, return of damaged goods to them. Response times are generally under 48 hours and replacement times are generally 1 - 2 weeks.
Support from the UK-based dealers is not so good for the reason @The Editor gave...little motivation to do anything other than point you to DJI. So to answer your question, why not? Probably because of customs / tax! They are pretty hot on imported e-goods atm so you'll probably find it's delayed a week or two and costs a bit more than you anticipated by the time you actually get it.