There are many 'consultancies' which operate the way you say. Whether you call them a body shop, rent-a-coder, or some other disparaging name, they are lousy places to work for exactly the reasons you state.
Keep the hope up. While the vast majority of places do seem to be body shops, they are not all that. There are still some actual consultant agencies worthy of the name. You just have to be both damned lucky and damned good to get into one.
And of course, some places are actually worse than a body shop. Some firms will suck you in young, bleed you dry with 100-hour mandatory work weeks (on a forty-hour salary) doing poor quality work, and spit you out as a lifeless husk. All the while you have to lie to the customer about what you are doing, lest they catch on that they are being conned.
Getting a job in-house is sometimes the way out of the fix you are in. For example, you are in one place long enough to learn both the first and last names of some of your coworkers. It can be quite a novelty!
The downsides of being in-house can include having to deal with more internal politics (contractors typically can avoid some of the infighting), or getting dead-ended into supporting some legacy pig of a system while the veterans get all the new development. So there is no guaranteed cure for the IT blues.