Because being frank here, most people I know who have had 30-40 years of exposure barely seem to understand the mechanics of the EU, how it worked or even how many nations it may have covered. Now of course this could be me just meeting a shed load of people seemingly all being oblivious, but I doubt it.
I guess it goes back to the initial comment you made of how if my younger generation was exposed to that many years of the EU then we would want to leave, honestly I doubt it, some would but I think firm majority would want to remain.
I think being born when we are already part of it and now knowing anything else may skew our perception and in turn is something the older generation may dislike seeing it evolve from what it initially started as, but I for one was happy with the EU as it is mostly.