Not necessarily.
They have been historically yes, but if there is no exploitable hole to find, it will not be found.
If it is hard to find and exists, it still may take longer than the device's lifetime to exploit.
I never said, that those holes were exploitable. I just said new ones are discovered. Some that were recently used were discovered back in 2007. However, those holes had no viable way to be utilized, so, they were shelved until they could properly be used.