Ever since the very first spoiled heiresses demanded to have their inbred faces immortalized, the brush-jockeys they hired have wisely decided to make a few adjustments. The artist got paid, the subject got a tangible representation of their overinflated ego, everyone was happy. The artist attending to the royal Medici family in the 1500s was known to paint his subjects to "highlight [the subject's] learning and social status," which is a nice way of saying "make them look less like peasant trash," and that was pretty much the standard at the time.
The truth is, we likely have no idea what anyone from that time period actually looked like. Every pre-Industrial historical figure could have had a big floppy dick growing out of their chin and we would never know. So let's just assume that they did.
Are you picturing it?
It didn't stop once photography became a thing. About two minutes after people started taking pictures, they started messing around with darkroom techniques to make s**t not look like s**t. If you think you need a computer to make someone look like a cartoon character, check out Joan Crawford kicking it old-school.
From left to right: hideous she-beast, beloved American icon.