I don't think it's that simple. I imagine that this is an issue of Korean, probably not unlike Japanese, lacking distinctive L and R phonemes. "Lew" is probably as wrong as "Ryu" because the actual sound is something that is not easily pronounceable for English speakers and because the proper sound itself is some sort of hybrid sound that is neither an L or an R and a softer y in the middle.
And if we want to get pedantic about it, I imagine that almost every surname or even given name in existence around the world is pronounced incorrectly to some degree just thanks to generations of linguistic drift, translation conventions, migration, and other factors. Like, it's easy to think "well, English names of historical importance are probably correct for modern English speakers because it's still English" but have you ever actually seen what middle English looks like? It's not totally indecipherable but it looks incredibly trippy compared to what we expect out of modern grammar and English structure and was pronounced vastly differently too (for instance "knight" was pronounced to include the "k" sound and the "gh" sound (which didn't sound like an "f" as a lot of modern gh words such as "enough" to).
tl;dr, language is screwy and while we were probably pronouncing it wrong the reality is that for a lot of people it would be borderline impossible to pronounce correctly. You literally lose the ability to properly hear and pronounce certain sounds not native to the languages you are primarily exposed to as early as 6 months old and into the beginning stages of learning to talk. Your brain starts being unable to detect differences and the physical attributes of your vocal cords and speech muscles work themselves to the point that they are actually unable to properly make the sounds.