User blog:DeadpoolN7/Why didn't the Alliance try this earlier?

So about 1/3 of the way through the priority Earth mission you are tasked with destroying one of the smaller reapers. You achieve this simply by picking up a cain and blasting it to hell. Now, the M-Cain was a relatively easy weapon to get in ME2, and they had two just lying around in 3. So my question is, if the cain was essentially a reaper killer why the hell didn't they just mass produce them, give them to each alliance soldier and say toddles to the reapers. It reminds me a lot of that scene in starship troopers where the fighter jets totally own a bug colony with no casualties but then continue to send regular humans in to get destroyed by the bugs.