We can enable more close reasons, but we are trying to hold off on doing that unless there's a demonstrated need because long lists have historically proven to be, at best, confusing.
At the same time, we certainly recognize that some sites have different needs. For example, Stack Overflow already has 5 off-topic reasons instead of 3.
What other close reasons would you enable if you had more than three slots available? Are they applicable frequently enough that just leaving a custom comment when closing just isn't practical?