Comment by ckozlowski

I'm just guessing here, but I'm going to bet that defensive ECM is probably deemed better effective per pound that CWIS.

It's worth noting here that CWIS' effectiveness hasn't really been proven. But what is certain is that it's theoretical effectiveness is being questioned as missiles get faster. The original 20mm CWIS had a pretty limited range. The Europeans went to 30mm with Goalkeeper, and now both are set to be replaced with either directed energy weapons (faster tracking, better accuracy) or systems like SeaRAM, which can engage further by switching to point defense missiles instead of guns.

I can see how directed energy weapons could be attractive to aircraft once the power density issues are solved, but right now they're simply too heavy.