I know someone who moved to the USA recently and learned English as a second language as an air and I had to explain this to them when they started playing Baldur’s Gate 3.
Western Fantasy is nearly entirely based on Dark Age and Medieval Europe, and for English speakers (in particular English speaking Americans) that usually means it’s based on England/UK in particular because it’s the country that speaks English.
So, a huge majority of fantasy characters have an English accent because it’s the accent associated with the only place in the world that spoke English during the vague target time fantasy is set in or based on.
Of course English sounded very different at that time in England, but the tie between them is so strong and has continued for so long it’s now the tradition/expectation.
Like, as an exercise, consider if you were to watch a classical Western-fantasy-type show like Game of Thrones or a Lord of the Rings series. If everyone had modern American accents (general, Southern, etc) wouldn’t you immediately notice and find it odd and out of place?
PS: the person in question was really quite great at English but had to install a mod to add subtitles in their native language because they struggled greatly with non-American accents.
It’s something that bothers me about bg3. Everyone is way too posh
Most of the posh sounding characters are posh, or at least formally educated. Gale is a wizard (clear enunciation for spellcasting), Astarion ws a magistrate, Wyll is the son of a duke, Minthara is a princess.
Karlac and Halsin aren’t posh and don’t sound posh. I’m not sure about Lae’zel, but that just leaves Shadowheart. Maybe Shar has a thing for accents?
clone wars and farscape teach us that oceanic (oceaniac?) accents come from space so it’s probably a character option in one of the spelljammer books
bachelor’s in recent runes from the university of fourecks
British: a giant enemy crab
Australian: a crab