I recycled an old query for Top tags with a high proportion of zero-vote accepted answers: quite a bit are around 20 % in StackOverflow. (Someone should check other sites.)
The top tag there has just one frequent answerer with 500 answers and 300 total score, but others often have the same pattern with a handful users, so it's not about individuals I think. Some are just unpopular tags but not all of them.
Is this a problem? The first affected things which come to my mind are:
- motivation of the users in the tag (chance that they disappear);
- relative motivation of the users (chance they move to more rewarding tags);
- meaningfulness of tag score requirements;
- meaningfulness of other score requirements for review privileges etc.