The extremely short answer is...
But let me get a little more in depth than that.
So if you haven't noticed, developers have been complaining about the used market a lot for the past few years. Essentially they're pissed because they feel like the used game market is significantly eating in to new game sales so much so, that they should get a cut of those used sales. Now first things first, whenever developers talk about the "used game market" they're not really talking about the mom & pop stores, they're talking about Gamestop. According to this 2009 Gamasutra article
Gamestop accounts for 21% of the U.S. video game retail marketshare (excluding accessories and PC game sales). That means almost a quarter of the entire industry's product is being sold through ONE retailer. ONE! I think a lot of you guys don't realize the power that comes with that figure.
Why the Car/Book/Whatever Physical Good Analogy Doesn't Work
The main reason is that they're physical goods. A used version of any of those things (especially a car) won't be in the same condition as if you bought it used. Used cars are going to break down sooner, used books might fade or have pages torn or water damaged, and used furniture could have rotted out or have weaker joints, so on and so forth. A used game on the other hand is going to play exactly like a brand new one and if it doesn't, you can get it replaced no problem. "Ok, so what about music and movies? They give me the same experience used or new too!".
Why the Music/Movie Analogy Doesn't Work
There are a lot of factors here but the main thing you have to keep in mind is how different the revenue streams are for these industries.
Let's start with music. I don't know if you noticed but the music industry is hurting right now. Actual CD sales are way down and that's mainly because people like to download their music (and the record companies were slow to capitlize on that). Because of this, the big brick & mortar stores that specialized in selling CDs have been shutting their doors left and right (Sam Goody, Virgin MegaStore) and, at this point, it's pretty much down to stores like Best Buy and Wal-Mart who sell CDs at a loss just to get you in the store to buy other things. At this point you realize there isn't much of a used CD market anymore because there isn't much of a CD market anymore. Artists (and increasingly labels) nowadays make most of their money from playing shows and selling merchandise, not the actual music. Video games don't have those alternate revenue options (not to those levels at least).
Now as for movies, you might say "Ok, here's a pretty comparable market. Movie budgets are comparable to video games nowadays and DVDs and BluRays are a comparable product since you might buy it and consume the experience once or twice before you're done with it. Why don't they complain about the used market?"
. That's because movies make the bulk of they're money on their theatrical run and the home market is just bonus to studios. It's become a bigger and bigger bonus over the years but all it really is in the end is an extra revenue stream for that product. Again, video games don't have that.
Why No Analogy Works
Again, no analogy works because no other industry has a Gamestop. There isn't one other industry where one company controls 21% of the market and consistently pushes the used version of the product they specialize in over a new one when the used version is an identical experience. That's why it just doesn't compare. That's why developers bitch about it.
So let's get some more shit out of the way.
"Games cost too much. Why don't they lower the price of games?"
Because those giant games you love so much (Uncharted 2, Halo, Metal Gear Solid, Call of Duty) cost a fuckton to make and unlike movies, the only money they'll ever see from it (until digital distribution is cemented at least) is if you buy it new. If you want significantly lower prices, than expect significantly different products whether that be shorter games, lower budget games, etc.
"If Gamestop is making so much money, why don't the publishers start their own stores?"
Are you fucking serious? Do you know how small the commercial viability of a Square/Enix store would be that only sold used and new Square/Enix games? Do you really think they could compete with Gamestop at this point because they would have to.
"Well they should provide more incentive for me to keep the game longer."
They are. That's why almost every game has multiplayer nowadays whether it makes sense or not. That's why almost every game has DLC. There really isn't much more they can do other than that. You're basically asking why movie companies don't provide more incentive to keep a DVD past your one viewing of the movie.
"What's the solution then?"
Ultimately there's only a few of options here. Digital distribution is one but a lot of you want physical copies of things. Developers getting a cut of the used market is another but a lot of you seem to have a problem with that as well. Publishers selling the games to retailers at a lower price point could help in discouraging them from pushing used so hard but I don't know if that's commercially viable for them (that could be another topic on its own). So yeah, if I knew I'd try to get the word out but the situation at this point is pretty complicated.
Do I want to see the used market go away? No. Are developers completely against the used market across the board? No. But you are kidding yourselves if you try to say any other industry is in the same boat. Gamestop isn't evil. They're just a company like any other trying to make as much money as possible but the way they're going about it at the moment is eating the industry from the inside and ultimately it's unhealthy for it as whole. You can't be pissed off at developers for that.