Because Russia is fighting a war, with the resulting casualties and destruction, right now. The faster they are stopped, the less damage is ultimately caused. George Bush, for the example you used earlier, is not currently doing this. So while he’s still someone who has gotten away with things he should not have done, time is less of essence in his case, at the moment. It’s like asking why it is more critical to attempt to stop an attempted murder in progress, then it is to work on investigating the one that someone else committed last week. Again though, the relative importance of them is not really relevant here anyway, because the discussion was about Ukraine and Russia in the first place. There are a great many bad actors in the world, many of which have faced no justice for what they have done, to include quite a few in the US, yes, and one could ask that same question about any one of them, whenever one of the others comes up.