Since there are not a lot of people actually celebrating Kwanzaa, the TV News folks are always out looking for Kwanzaa celebrations to tape. In the last dozen years, I have never seen a Kwanzaa celebration that occurred in a community center or church that did not include a few white folks. (The Kwanzaa celebrations that occur in people’s homes aren’t going to have as many whites, obviously.)
The only thing that makes Kwanzaa appear exclusive is that no one has figured a way to make a dollar on the event.
Everyone can get drunk on St. Paddy’s day or at Oktoberfest or eat egg rolls on the Chinese New Year and party down on Cinco de Mayo because the bar owners and restaurateurs want to make a buck and they invite everyone down to spend money. Everyone can turn out for a good time for the Feast of the Assumption in Little Italy or at the local Byzantine or Orthodox church for the Feast of St. Nicholas because those (generally church-sponsored) events are being used to raise funds for the sponsoring organization.
Since no one has bothered to set up a money-making hook for Kwanzaa, people tend to leave it alone. This does not indicate that it is exclusive; it indicates that it is ignored.