It's not up to them. It's up to the prosecutor's office. Like Wayupthere stated, this is a very common tactic used for far less crimes. Go study how the criminal justice system works these days. The basic ploy is to slap as many charges against someone arrested as they can come up with, even for a simple bar fight. That gives the DA office plenty of room to plea bargain with the defense, who is stuck either accepting something or risk their client -- many of whom can't afford better counsel for drawn out cases -- going to a jury trail with all the charges weighing over their heads. It's a risk the DA knows 99% of the accused will never accept. Thus, the scales of justice are greatly swung in the favor of the prosecutor.
This strategy also provides the DA office with excellent stats when it comes to showing the public, who are going to vote for these DA officials, how tough they are on crime. Thus, there is a huge incentive never to change this policy.
The downside is society pays for this. We end up with a slew of people with "minor" crimes forever having the label of felon on them, thus having more difficulty finding a job, and thus takes them out of the taxpayer pool and into the welfare pool. And, we have a massive jail population again for "minor" crimes, which again takes people out of the taxpayer pool and into the jail subsidized pool which costs taxpayers way more money than it costs taxpayers for welfare support. Yet, the public loves to jail people instead of educating them...