I've tried to find a section about control systems in here but no luck. My question is why there is no control system section in here.
As noted by @psubsee2003 in the comments, there was a proposal but it was also closed because it didn't have enough support to be launched.
You can think of restarting the proposal, but chances are great that simply not enough people are actively interested in the subject to support a dedicated Q&A.
@jonsca also suggests https://dsp.stackexchange.com/, which might be suitable for basic questions.
I restarted the proposal here. Please join if you would to like to see an active Q&A site for Control Theory.