Because you can’t.
/all is an amalgamation of our entire community (sans /removed). We don’t want it to become a random dumping ground primarily because it’s way too difficult to establish rules and moderate. When you submit, you can type any word into the community field and (hopefully) find an appropriate spot for your post. You can also look at our world to get a bird’s eye-view as to where it might be appropriate.
If you still can’t find a place, why not start your own community? We're sure /RandomDumpingGround would be a great place to give and receive value. Don’t let the discovered need go to waste.
We’re not entirely sure it’s appropriate to call this the Frequently Asked Questions area as, candidly, we don’t keep track of how often these questions get asked. Consider this community as a place where we post answers to what we anticipate your questions will be. But, if our crystal ball is malfunctioning, feel free to post your question in /GettingStarted/Help. If we turn your question into an FAQ, we’ll credit you back the karma to post it. It’s the least we can do. We also welcome suggestions at /GettingStarted/SuggestionBox.