The prosecution has the full backing of the state and for all intents and purposes has an unlimited budget. The accused often is stuck with an overworked public defender. The odds are against anyone whether innocent or guilty once you’ve been arrested. There have been plenty of instances of dirty cops get caught planting evidence on camera, prosecutors withholding evidence, and striking people of color from juries because they thought they were less likely to convict and (rightfully) who are less trusting of police.

Taking all that into account, a known lighter sentence makes more sense than an unknown heavier sentence.