Why do people never mention the glitches in The Witcher 2 where you have load of quests to do but get to a certain point in the game then all those quests auutomatically become failed quests why

Are you sure they are glitches and not simply a case of you advancing the game along too far. For example, you have to do the Act I missions like destroying the Necker nests and the insect queens, during Act I. If you advance to Act 2, those are all failed. Other events can cause previous sidequests to fail also depending on what happens. One event can cause a certain character to be killed, which will cause you to fail any task he might have set you.