As for Runaway Brain, I remember being disappointed when it wasn't on the laserdisc of the so-so A Kid In King Arthur's Court as it had been on the theatrical release. At least when it lost the Oscar for Best Animated Short Subject (i.e. anything shorter than Saludos Amigos), it lost to a Wallace & Gromit short.
Maybe this is the first in a series and they're saving it for another release.
Maybe this is the first in a series and they're saving it for another release.