Royal Mint issues unique 5-kilo gold coin (yes, that’s about 11 pounds!) Sorry, it’s already sold

According to the BBC [link] the Royal Mint has issued a new series of coins highlighted by highlighted by a unique 5-kilo gold issue. Apparently only one coin was struck and has already sold in excess of £100,000. I can’t help but wonder why they didn’t strike at least a handful of them.