That is a shame to hear.....perhaps they didn't plan for the care *after* the relocation.
Our rescue manages a herd of rabbits between 40-50 at any time and they have remained healthy and disease free. They live in a communal environment.
Like with any animal however, there has to be a set day for health checks, regular grooming (coats, nails & glands) as well as vetting and speutering.
Maybe this step was left out and they were left to just exist as if there were no human intervention....and in nature, there is a shorter life span and more deaths than rabbits that are cared for by a caretaker.
It's sad to hear this but without more information I don't want to make any more assumptions on why this may have occured.