There is a particularly damaging rule of professional responsibility for lawyers: they're not allowed to lend money to their clients, even when those clients are good credit risks: poor but have a very high chance of winning a case worth a lot of money in the near future. That enables rich defendants to pressure poor plaintiffs to accept settlements at worse terms than they otherwise would; it's the easiest thing in the world to delay the resolution of a civil suit. The family of the decedents requested a lenient sentence because the family of the defendant promised to settle their wrongful death civil suit immediately. If lawyers could lend clients money, you bet your ass the family of the decedents would have been clamoring for jail time, not leniency.
Here's the tougher situation. Same deal, but the defendant has no money on hand, but has a rich career ahead of him. If you let the defendant out of prison, he can make money, and that money can then go to the family of the decedent via the wrongful death suit. If he stays in prison they never see a dime. Criminal cases are supposed to vindicate the rights of society, but it's tough to say you're doing that when you leave the victim of a criminal act in a worse position than they otherwise would be.