Why would foster parents be denied to adopt their foster children?

truthfully, I've never heard or met any fosterparents, who were denied adopting their foster children, once they were adoptable. my husband had the same fear about our VERY SOON to be STAS, because he is 55, and our little man is only a baby, (well, he was a baby, NOW he is already 18 month old) but we were assured that that is NOT the case :) I know of 2 VERY OLD grandparents, who were fighting for placement of a newborn grandchild, that was never placed with them (BM chose a religious adoption center, and child became never a 'foster child' but went straight for adoption) and I must say, I was thinking to myself WHAT would those people do with a newborn???!!??? they are both at least 78 or so.... instead of FIGHTING, they should have tried to establish a relationship with the AP, and be GRANDPARENTS to this little one... so sad, for all involved, but that's how it went down... again, this had nothing to do with CYS PLACING a child, this was a straight adoption situation.