Why are UK sellers almost universally out of stock on modern cards?

I've searched up so many cards for various deck types- milling, zombie aggro, white blue Az, red goblin, eldrazi... and all across the board only one or two cards per list are actually held in stock by UK providers (chaos cards, magic mad house, etc) with everything else listed as unavailable.

Yet sellers from the US and some continental EU never seem to have shortages? Even commons or bunk rares are out of stock for a lot of these places, only money cards never seem to move.

Is there a particular reason the UK secondary market for magic is so dead?