I know you might be asking rhetorically, but I’m still going to attempt to answer:

It’s because the show runners and producers are predominantly white and didn’t care about Asian accuracy— “they all look (and sound) the same”. Simu Liu probably unknowingly added to the mix in the sense that all he cared for was that there was finally a show about Asian culture and representing being made, so he jumped at the opportunity despite the cultural differences (Liu being Chinese vs. The show being about a Korean family)