I don't know never really paid attention on how much time/money/effort it takes to add another category. Last years Alafia ss cat had a good turn out.
Just read into what RTR posted above and you can see that they are yet another race series that has decided the cost/benefit of a single-speed class just isn't warranted by the turnout (or lack thereof) of the SS'ers out there.
I don't disagree that would be 'nice' to have a single speed class but when the SS'ers don't come out in enough numbers to justify it, then it is really is in their best interests to drop the class.
If you really want a SS class so bad, have enough people come out to make the business case for them to add it.