as has been said previously, its not the lack of interest. Its the royalties involved. Microsoft owns the Halo franchise. Megabloks got a contract to do lego of it. But to do plastic kitsets would end up being cost prohibitive.
"I am a leaf on the wind, watch how i soar"
Recite the litanies, fire up the Gellar field, a poo storm is coming 
Check out my blog here.