Because if you read the conditions of use for Garmin software they absolve themselves of all responsibility for foul-ups. It may or may not be legal in the UK but who's got a big enough wallet to take them on? In my case they want just under £78 for an exchange unit.
Try http://www.ukecc-services.net/ They should have enough money to take on Garmin.
Hurry though, you'll only be a member for a few more months.