Me lecturing them for hours was never going to work regardless but I dislike the idea of coming up with so much information (which was very fun for me not a chore) and never using it
I think [MENTION=7006]DEFCON 1[/MENTION] is right to an extent - you can't unilaterally force this sort of thing.
But that being said, I would nevertheless say: don't despair! Just think about how you can introduce the info in play.
Another example of that, to add to some of the other good ones in this thread: in my game there was a brief episode where the PCs travelled 100 years back in time and helped resuce a wizard's apprentice who had been caught up in a historic crisis. The PCs said their farewells to her, and then returned to their own time. Several sessions later, when the PCs were going to have dinner with a baron, I wanted to bring the rescued apprentice back into the game. So I told the players that, when they sat down in the baron's dining hall, they noticed, in his series of family portraits, two that caught their eye: an old portrait depciting a middle-aged woman who otherwise greatly resembled the young apprentice whom they had rescued; and a recent portrait depicting a young woman who was the spitting image of the rescued apprentice.
Some conversation over dinner revealed that the young woman in the recent portrait was the baron's niece; and that the middle aged woman in the old portrait was the baron's grandmother - which fit the timeline for the rescued apprentice. Further adventures revealed that the niece was in fact a Vecna-ite necromancer; and also that Kas had been trapped by, and was now seeking vengeance against, the apprentice/grandmother - who had obviously grown into a powerful wizard, probably also a necromancer. The PCs swore an oath to Kas to track her down, but haven't done so yet - they've had other, more pressing, business - but have since learned that a powerful dragon, whom they ended up killing, also had some sort of grudge againt the apprentice/grandmother. (The dragon tried to negotiate during the fight that led to its death.)
So quite a detailed backstory has not been wasted. It's just that it comes out in fits and starts, as suits the adventures and the players' interests, rather than as an all-at-once download. And as the GM I can amp the whole thing ump anytime I want to by having the mysterious apprentice/grandmother suddeny turn up! Or dropping another clue to her whereabouts, or to her activities in the 100 years between the PCs rescue of her, and their present day.
It's a shame ENworld doesn't have the Xp system they used to because there are some really good ideas.
You can still give XP via the green star button at the bottom of a post.