They don’t stay in the open in tight-packed columns for long; they’re poorly-trained, not completely braindead. The AFU were likely waiting to see which tree line they were going to set up in, then struck.

It stops Russians from shelling Kherson.

Did you know that a lot of military success cone from being able to hit the supply chain and backing troops that support the front lines?

This is demoralizing for Russian troops because they are not safe training and assembling behind the front lines. They are always in danger.