Why would a judge do that in the first place?

Or if they do, what prevents either side from going to the next court to get it overturned? And the next court after that

Idk if this is everywhere but the system I’m used to is this: the first two levels of court look at the case details in-depth, then there’s a third ‘last resort’ court for if you think there was a mistrial (this usually gets rejected), and they can send it back to the second court to re-do if something crazy happened that’s not in line with correct procedure as it sounds like it did in your example

If we don’t trust a whole series of judges to pass judgment fairly, then I’m not sure we should have judges. Personally I trust these more to apply laws and case law than if we’d put elected politicians on the seat of judge, as basically happens with them choosing the sentence parameters (and as you see more and more often in my country; older judges also speak of higher and higher sentences being expected, makes me wonder if we’ll go full-circle to medieval practices eventually)