When presenting a criminal defense, you have the right to ask the court to dismiss the charges filed against you. In fact, this is a pretty common play for a criminal defense attorney to try even if they don't feel it has a high chance of succeeding. There are, however, at least three good reasons why a judge might agree to dismiss a case.
As a criminal charge is brought to court, the prosecution has to handle a number of little steps the right way. While the court won't toss out egregious charges over minor infractions, the right judge may be willing to dismiss something like a disorderly conduct charge. Suppose, for example, that the arresting officer didn't fill the affidavit out properly. This is oftentimes the strongest bit of evidence in a disorderly conduct case, and making a mess of the affidavit opens huge questions about what else a cop might have gotten wrong.
Police and prosecutors do not have unlimited power to trample people's rights, and some judges frown upon the slightest hint of such behavior. If a case involves difficult questions regarding when the police have the right to search a vehicle, for example, that's a pretty good starting point for a potential dismissal. A police officer might have pulled a driver over and failed to establish reasonable suspicion or probable cause for a search. This happens in plenty of drug cases, and it's definitely something every criminal defense attorney wants to discuss during preliminary hearings in such cases.
This can be one of the weirder scenarios. Sometimes, a prosecutor just decides the case is blown and hangs up on it to avoid making an uglier show of it. This can happen, for example, after a discovery request shows that the police lost track of a weapon supposedly used in an alleged assault.
Where it can get weird is when prosecutors pull the plug to avoid damaging other cases. Suppose your attorney started looking into wiretaps that were used to justify an arrest. If the prosecution feels that exposing the full details of the wiretaps might endanger a bigger case, they may ask for your case to be dismissed to avoid that embarrassment.
A criminal defense should try to turn over every stone. Even if you think the prosecutor has an ironclad case, it may be worth making them show all of their cards.