Jury trials are expensive as fuck, and you don't get a penny of it back if you win.
The most common offenses charged are less-serious things like DUI, where first offenders are likely to receive penalties like a fine, maybe a very short community service, and probation.
If you go to trial, you always might lose, and you will pay $50k of legal fees.
If the prosecutor offers you a $10k fine, what're you going to do?
Even if you could raise the $50k -- of you go to trial and lose (which is always possible), you are likely to get close to the maximum penalty for having fought.
Probably a lot more than we'd like to admit.
> just because they don't have the resources to fight the charges.
It's not just that they don't have the resources. It's also a matter of risk assessment because a jury can be fickle. Lets say you have 20% chance of conviction and 80% chance of acquittal. The prosecutor offers you a plea deal for 1 year ( you get out in 6 months with good behavior ). If you choose to go to trial, the prosecutor says he is going to charge you with everything he can and if found guilty, you go to prison for 25 years. What do you do? You have 20% chance of spending quarter century in prison. Or you have 100% chance of 6 months ( 1 year at the max )? I think most people would choose the latter.
> Quite perverse incentives.
In a way. The system incentivizes plea deals because the prosecutor doesn't want to lose cases. So he only wants to try cases that are open and shut and go the plea deal route with the rest.