Not quite true Easy. The CWS is being fitted as mitigation for all MAC risks. Cat A airproxes have occurred with CAT, whether they had TCAS or not, and whether the Mil ac has been squawking or not. The likelihood of the occurrence is of course a factor, but a large part of the impetus of the programme being re-instated came from the societal risk of a Mil-Cat collision and the asymmetric response that it could create. Mil-Mil (and the sub-sections within that category) are more likely due to more flights taking place in uncontrolled airspace, but with air congestion and fast/pointy aircraft operating close to busy controlled airspace, airproxes and the possibility of MAC exist and happen with increasing regularity. The Cost Benefit Analysis of CWS vs CAT would probably concur with your view that "there would be absolutely no case for the fitment of CWS", but the reality of the situation was that this spectre was the reason it was reinstated after the SDSR.