Making them public lets Russia know we're aware of their actions, which in turn may drive them to greater efforts to make these actions harder to detect and therefore harder to defend against. I also wonder if making these public, detrimental and unnecessary, is just a cynical ploy before an election to give the appearance that this administration has been tough on Russia, when actual toughness on Russia would mean not just indictments, but also sanctions and other tangible consequences.
On the other hand, absent legal accountability for these individuals and Russia itself, making these indictments public allows the rest of the world to see & know what Russia is up to. That might facilitate action through the softer power of diplomacy, and perhaps also put other countries on notice that they must take greater care in protecting their critical systems as well. And if it is the correct choice to do so, then any political benefit, cynically motivated or not, is an ancillary factor.
I suppose it may be a tough balance to strike. I think I come down on the side of making these issues public knowledge. Just as I similarly believe bad actions on the part of the US should be available for public scrutiny whenever it does not jeopardize the lives and safety of those who fight for our country.