Question about Mom’s and Joey’s

Through the years, I get mom opossums with joeys in her pouch. At the point the joeys are about 4”, they start falling out of her pouch and I watch on pins and needles for them to crawl back in her pouch or on her back so they aren’t left behind. The other day I found one 4.5” long and took it to wildlife rehabilitation center. Here is my question. I read that at 4” or 4 1/2”Mom does not leave them in the den while she forges for food so why is it that over the years once they start falling out of her pouch at 4 inches, I never see her with them again and I never see toddlers from her grown litter that come to the feeding station. Is she losing them all one by one as they fall out and are left for prey? I’m watching her now eating and she has no joeys in her pouch or her back,