L.S.
I used to work with a program (private) that focused on gifted kids. There are a lot of possible explanations for the focus on the hypotonia rather than the academic subjects. First, the teachers may feel that they need to focus on his fine motor skills first and foremost as this is the window of time in which the most can be achieved in helping him. Also, they may see the handwriting issue as an important first step in any kind of academic acceleration. It is also very likely that the is not much funding for gifted programs at your school for this age....many times there is one special needs budget and the gifted programs get cut before the other special needs programs are cut, which is understandable, but frustrating. FInally, they may want to make sure that your son is not overwhelmed. There is a lot of non-academic content to learn in school for a five year old, with or without special needs and giftedness being part of the deal. I also think it is important to not become super focused on the "gifted" identity when your son is so young. We tend to like to label kids so young and even a positive label can have negative consequences. In the case of giftedness, it can put a lot of pressure on a young child. I would only suggest that you intervene with special curriculum at this age if your son was starting to exhibit disruptive behavior due to being bored in class, which he does not seem to be doing. BTW, many private schools have even less to offer gifted kids and definitely have a harder time accomodating the needs of special needs kids.
A lot of research shows that at this age, parental enrichment can be very helpful for gifted kids. Take your son to museums and concerts. Read to him. Watch history videos with him. Make it fun and let him take the lead with what you explore. If you have other children, they will benefit from this as well.
I am basing all of this on my own teaching experiences, the fact that I was placed in a gifted program as a child (when CA had such a thing) and also the fact that my eldest son is gifted. He is now 12 and we are definitely in the situation that he needs more stimulation and acceleration and so I want you to know that I really do understand your concern and frustration. Gifted kids do need more attention than most schools provide, but you do have a bit of time here. It does sound like your son has great teachers and you are already doing a great job.