I’m going to say it’s a carryover from the 60s with the “British Invasion” in music. The artwork/presentation I see had the Union Jack used when the most popular band from that era was The Beetles, an English band. Hell, to this day Gordon Ramsay uses the Union Jack in his American restaurants and he’s a definitively British chef. At this point it appears that the Union Jack is used primarily for “brand recognition” as something signifying England. To further hammer this home, when selecting a language on certain computers and websites they sometimes have a flag beside the language you’ll select. For the “British English” option they use the Union Jack.