I think it's one of those things that only sticks out to you if you're constantly seeing people who don't look like you in the media. I'm not in that situation, so that's just my understanding from what others have said.
And yeah, if you're not in that position and therefore don't think of it then it's hard to firstly remember to aim for that character variety, but also to know how far to go with it. I'm not familiar with [X], so should I write a character who is [X] and would it be taken as representing them badly? Is that better or worse than not at all?