Because they want to appear nice. Some people on the other side of the stereotype are sensitive about it, can take a serious issue with the stereotype itself, and no one wants to be accused of stereotyping. Notice though, that you said yourself that stereotypes have “some” accuracy. They are not true, they are just somewhat true, as far as averages go, but they don’t necessarily apply to the person in front of you.

I am a good example of that. I am Russian and Americans love to point out that Russian people drink a lot of vodka. I have never drunk vodka, I always hated it, but even though I have, of course, always known that this stereotype is true, it was still unpleasant to me when it appeared like someone assumed that therefore I must like vodka or drink a lot of vodka myself. But guess what? I don’t assume that anymore, so if someone said to me that Russians drink a lot of vodka, I would simply laugh and say “Yes, they sure do”. Even if someone said directly to me that since I’m Russian I must like vodka and drink it every day, I would still just laugh and say “I personally don’t, but there are definitely some Russians that do”.

Stereotypes are only as painful as we are willing to make them. Some people love to take offense, so others learned to be careful. All stereotypes are “somewhat” true, statistically, when speaking about a group, and have no relevance whatsoever with regards to the actual person you’re talking to until you actually find out if he conforms to the stereotype or not. Then you can both laugh about it, kindly.

To not get lost in stereotypes, whether they seem to apply to others, or yourself, treat yourself as an individual, not part of the group, any group. Then you can treat others as individuals also, and stereotyping will cease to be an issue.