If the CTA endorsement went through, being an endorsement it'd be optional. If someone thinks it's a PITA, then they pretend the option doesn't exist and life is the same as before. If someone wants to be able to operate in CTA (or even just to do the odd Class C transit to avoid bad weather) then they can do it. If instructors don't want to bother with the training then they don't have to offer it.
It's no different from any of the other endorsements they offer, ranging from simple radio, to wobbly-prop, glider-towing, formation, low-level flight or float endorsements - you don't see RAA members saying "this is all too complicated and expensive, save us from these endorsements". The training syllabus and associated documents are already written so no added expense there. Worst case the RAA could charge people applying for the CTA endo a small fee to cover the extra bookwork.
I also would be amazed if participation dropped, if anything the additional freedom would attract more pilots, which means more money to the RAA and increased political power.
Let's assume that it takes an RAA pilot 10 hours to do their CTA training. It'd cost maybe 10x$200 + maybe the cost of a medical (another waste of money but evidentally politically required). Call it $2200. Please let me know how much you think it would cost to get a PPL. Real-world figures please - factor in the more expensive training, extra textbooks, cost of the exams, medical, cost of the flight test, etc. Also assume that the RAA instructor already knows what you are capable of, but the GA instructor doesn't know you from a bar of soap.
Why aren't glider pilots required to get a PPL?
Edit: Yes I know you can get a PPL then use it as a CTA endorsement. As I said it makes as much sense as requiring a bus license to be allowed to drive your car on the highway.