Why isn't there a subforum specifically for tuning?

 

I guess because it has never been requested/there is no need.

There is Under The Hood, and Fixed Induction, most tuning stuff goes on in those

 

Or the ever popular JDM Tuning forum.

Between Under the Hood, Technical (a sub-forum of UTH), Forced Induction, and JDM Tuning, it would seem there are more than enough places to discuss "tuning" of any flavor.