Because in large companies, any helpful suggestions get lost in the noise. Everyone has opinions on how things could be done better, but very few of them are good.
The discussion forum still has to be managed (I said "anarchy" facetiously) and at least minimal standards of professionalism would still have to apply. And if the board still devolves into a swamp of griping and bickering, then well, they can nuke it and at least say they tried.
Most ideas are indeed crap, and the good ones have to be picked out. But reducing the total number of ideas doesn't raise the percentage of good ones.
I remember a company I worked at that an internal website for suggesting ideas. The problem is that the management never looked at it. And because of that, employees stopped posting to it. And that was that.
Most ideas are indeed crap, and the good ones have to be picked out. But reducing the total number of ideas doesn't raise the percentage of good ones.