I get that they'll want to avoid the embarrassment of imprisoning their former president. But aside from the fact that I think having Trump as a president has been seen as a massive embarrassment anyway worldwide, if they don't make a very firm statement that it's not ok to sow widespread doubt on a presidential election with no proof, then every president can try to pull this when they lose.
You basically make a martyr of him if you throw him in jail. You would basically fuel a large segment that he was witched hunted for for what he has done instead of just showing how baseless his attacks are. An ex president in jail does not solve anything and it would not suddenly make the people who follow him suddenly drop him. Also for most of these crimes, jail time would not really be long enough to pursue. The the only real thing you probably going to get him with that is criminal is tax evasion and that's really not going to do much. This is why I am saying it would never go to court because if NY had the goods, a plea deal would be done and it would be over.