They’ve got a slightly different business model to TK Maxx.
They don’t hold stock.
They are essentially a shop window for distributors/manufacturers to clear out their items without the prices being searchable on the internet or other shops having to price match against them.
So the stuff to be sold, gets put on sportpursuit, then once the ‘sale period’ finishes, they process all the orders at once and send it through to the distributor/manufacturer. So far things I’ve bought have come from Sportpursuit themselves, but I wouldn’t be surprised is some items are shipped direct from source.