I blame Shakespeare, to be honest. People hear how people talk in Shakespeare plays and decided that was an accurate record of how people actually talked back then because....I realize common conversations weren't really recorded until fairly recently so nobody really knows how people talked day to day but theater tends towards the dramatic while letters tend to be formal.
I've been reading the Stormlight Archive by Brandon Sanderson and I do appreciate how it feels like the character talk like normal people while not making the mistake of sounding too much like something people from our world would say.
I was watching the show Carnivale Row, which takes place in a world not ours but with obvious parallels. So there's a full season taking place in NOT-Victorian London which is fighting the NOT-Crimean War against NOT-Russia and then out of the blue one of the characters mentions the world "Pharaoh". Which is a reference to a very specific ancient earth culture and comes across as Jarring as hell.
Actually, people talked even worse than that. Here's an excerpt from 'Time Travelers Guide to Medieval England.'
"Dame, what hold ye the ell of this cloth? Or what is worth the cloth whole? In short, so to speak, how much the ell?’
Sire, I shall do you to reason; ye shall have it good and cheap.’
Yea, truly. Dame must me win. Take heed what I shall pay.’
Four shillings for the ell, if it please you.’
That were no wisdom. For so much would I have good scarlet.’
‘You are right, if ye may. But I have some which is not of the best which I would not give for seven shillings.’
I you believe well. But this is no such cloth,of so much money, that ye know well!’
Sire, what is it worth?’
Dame, it were worth to me well three shillings.’
That is evil-boden...’
But say certainly how shall I have it without thing to leave?’
I shall give it you a tone word: ye shall pay five shillings, certainly if ye have them for so many ells, for I will abate no thing.’
Dame, then what shall avail long words? "