I have to agree with the OP... I think that in a forum such as this you need to support the major platforms of Apple. I see CarPlay as being very similar to HomeKit, and you have a forum for that. In the past, I started and operated a tech forum that was pushing a million unique visitors a month... much smaller than MR, but large enough to understand forum-think.
I just jumped into CarPlay this week with researching and installing a system for my truck. I found that the information available was scattered all over the internet and had a number of bumps trying to get everything to work. I'm sure if there was a dedicated forum here then that discussion would be centralized here. For example, a lot of the discussion about CarPlay was on Apple's own forums... there is quite a bit there. I ran into an obscure issue that drove me crazy for hours that prevented my iPhone 6s Plus from working, but my daughter's iPhone 6 worked with it fine. Apparently a parental control restriction can be set to disable CarPlay... I don't remember ever setting parental restrictions and ended up having to reset my iPhone as a new device to get around it. While this is an iPhone issue so to speak, it was also tied to CarPlay and I would have much more easily uncovered it had it been discussed in a CarPlay forum here. As such, I took my discussion elsewhere since there wasn't a place here for it. So the next person that runs into that problem, and there will be many I'm sure, will go elsewhere to discuss it.
its ultimately the MR Admin's decision, but you are missing a big opportunity. CarPlay is expanding very rapidly if you look at the long list of car makers jumping into the fray. You miss establishing yourself as THE place for CarPlay discussion when it starts out, you may never get it back. That is the way tech forums lose some of their relevance as tech shifts over time. I understand too the hesitance to have an inactive subforum that appears inactive or "dead"... people don't post in them. But hard to see CarPlay not taking off if there was a place for it... status quo will be that you continue to see no demand if there isn't a dedicated place... and those people will go elsewhere to get help.