It's actually a flaw in OBS that recording will not stop automatically before the disk gets full, but it's also not entirely trivial to implement, because the definition of "disk is full" varies. If it is actually full with 0 bytes left, it is too late, because the video file cannot be gracefully finalized in this case. If you leave some headroom, how much? The requirement of this headroom varies greatly, depending on the bitrate, which is not always constant. It also takes some more bytes in the output between the decision to stop the recording and until the finalized video can be closed.
I'm boring you, I know, but developer's time seems to be spent on real streaming features and not on something the user has to deal with in the first place: provide enough disk space.