They are - we're all bodhisattvas. The question is when does one realize it.
The root of all suffering is ignorance: chiefly, the ignorant perspective that we are not all unified consciousness. It takes most people many many lifetimes to access the path of understanding (dharma) and, typically, quite a few more to progress along it to the point of authentic perspective (what we simplistically call "enlightenment"). All are equally discovering their Buddha (empty/unified/infinite) nature, though at slightly varying paces.