They dont have tools, dont know what to do. But more importantly, someone who was in the same situation or did not studied it a lot is simply incapable to truly understand. They can nod, listen, validate, but wont be able to puzzle out half said things, badly expressed things. They won't be able to see logical consequences of what you talk about unless you point them out.

Meanwhile, someone with the same experience, even if not friend, will be able to understand much more and more easily.

It is not so much about some moral or relational failure on their side, it is simply that it is impossible to imagine feelings and situations you never had.