Recently, a bunch of different governments put out updated guidelines for closings during the worldwide outbreak. Pretty much anything considered vital has been closed down. To comply with all these new regulations, Games Workshop is closing down their locations and to make sure that they're not spreading it via the mail, they're limited online sales as well.
From the post:
The safety and wellbeing of all our customers and staff are paramount to everyone here at Games Workshop. In response to the developing global situation surrounding the spread of COVID-19, and following the advice and instruction from both the government here in the UK and throughout the world – we are closing Games Workshop sites around the globe.
This means that all our Warhammer and Games Workshop stores will be shut from the 24th March until an initial date of the 14th April. We’ll also be closing our factory and distribution centres – so our online stores (Games Workshop, Forge World and Black Library) won’t be selling or shipping any physical products during this period either. If you’ve recently placed an order and are waiting for it to arrive, please give us 48 hours to contact you. If you’ve still got questions after that, then please drop our Customer Service team a line via email, they’ll be valiantly working from home to ensure you’re supported over this period.