Then you can add them explicitly. And what about /proc and /dev? And /sys? And /run?
You usually know which mounts you want to go into, but don't have a list of every single one you want to stay out of. Most people want a whitelist here, not a blacklist.
Most people don't want to give a thought to whitelists or blacklists, they just want to find the files relevant to them. Most people are using grep or another command piped from find, and doing 'sudo find /' (sudo to get rid of all the errors from /proc) is the easiest way to search everything.
99% of the time sys and proc and run and all that stuff won't even show up in the filtered results, and if something does, its an easy 'grep -v ^/sys' to exclude.
