Those slaves who deviated even slightly from the secret knowledge Cryala gave them were quickly found and dominated by the Hive Mother. There were still many, though, who lived the lives of beholders, typically gaunts. The Disciples of Luumu discovered many in secret meetings in the night, but they rarely turned them in...
It seemed that, being of the 'Lesser Races' themselves, they often felt a pang of sympathy for their fellow fleshy ones. When those who were oppressed were given the chance to become the oppressors, as long as they didn't make to many waves or try and rise too high, they were most commonly left alone. Their offspring were of strong (if not a bit sensitive and emotional) beholder stock, so what was the worry?
The beholders who had taken their hunger too far dwindled in number, and the more common (and more socially acceptable, given the amount of gaunts that weren't of beholder minds) method of feeding on slaves became to simply drain little bits of life force at a time (as opposed to wholesale soul-devouring). This new process was a bit slower for the beholders, but it left the slaves livelier afterward and far less cooked or undead than in the past.