Why not ask the sires?

I understand that a Lot of sires lie or don't know themselves, but why would low generation "Young" vampires don't know about the antedilluvians? Like therese voerman is 6th generation that means her sire was the grandchild of malkav why would her not ask about him? And IF he did not know why would he not ask his own sire? Or why would a childe of gratiano not ask about granpa lasombra ? There should be quite a Lot of vampires that know about the 3rd generation and i mean "know", like How they acted How they ruled if they had pets not simply know that they were real, vykos should have met tzimisce or one his childes be the dracon,byelobolg or yorak, a Lot of kindred should have knowledge about the ancients, a handful of Giovanni should have met cappadocius and some temerei should know one or two 4 or 5th generation vampires