District attorneys offer plea bargains for numerous reasons.  One reason is the cost of taking a case to trial.  Also, the time and cost involved in a trial would make it impractical for every case to go to trial.  The evidence also would be a factor in determining whether or not to take a case to trial.  There may be sufficient evidence for a conviction on the charges and a plea bargain may be offered instead of going to trial.  A criminal record may result in additional time if convicted of all current charges and therefore a plea bargain on lesser charges may result in a shorter sentence.  If the defendant has provided evidence against others involved in the crime, the district attorney may offer a plea bargain on lesser charges.  If there is insufficient evidence for a conviction on the charges, there may be sufficient evidence for a conviction on lesser charges which may result in a plea bargain.