There is the option to vote for a close because of length or low quality. What is wrong with answers like this one. It's short but useful therefore not really of low quality. What's wrong with those kind of answers? I think it's OK to give a one-liner if it has new and useful information. Also closing this stuff isn't increasing our multiple-answer-ratio.
Short answers can be useful, yes, but the vast majority really aren't, which is why the close reason exists.
Remember numbers of questions and answers are only one set of metrics. We also need quality.