I suspect Almost Human need to tally up the pre-order sales after release date and bank the money before considering any physical merchandise.
An issue with merchandise is international delivery charges and potential border/custom charges on top again.
Most of the stuff I've seen like T-shirts have been via a 3rd party who just stick the design on a generic cheap template T-shirt, so I imagine the percentage Almost Human would receive per sale would be very little compared to the potential loss if they ordered 500 unit run but only sold double figures (don't know if that's how it works or not). And I know for sure I wouldn't like to be stuck with 500 mugs if the demand wasn't there, or put off by total delivery price, unless I was very clumsy and broke my mug every day so would appreciate the guaranteed supply in the office.