Mr. Blaze said: "But my question remains why was it left off the album?"
Probably to save it for their The Best of the Cowsills compilation, released mere months after this LP (and just in time for the Christmas shopping season!) Makes good marketing sense, anchoring their greatest hits with a track not on any other LP at that time.
I wonder when "Poor Baby" was left off this album release, especially after it was their most current record out before the albums release. Perhaps it just doesn't fit, to be honest I never thought "Poor Baby" was a good single track, it could've worked as an album track or B-side tune, but I really don't think it fits on this release. But my question remains why was it left off the album?