Why are creators obsessed with giving Wasians freckles?

Because Lucy Liu is a model of perfection in her characters: smart, brash, tough, capable, freckled.

I've never been interested in her genetic make-up, so I realize I don't know if she's 'wasian', but if I had the option to create a face and freckles were the option, there would be freckles.

TL;DR - because they can.