My guess is that part of the goal is that, having bled Russians dry, they're looking to have another intact economy to loot. They are aware that the more they break, the more expensive it'll be to get Ukraine into full milking condition.
So this means scale the invasion upward gradually.
First, hope that shock and awe will result in immediate surrender with minimal damage.
OK, that didn't work, so maybe scare them a bit with an armoured column of death.
Darn, that didn't work, OK, idunno, hit some infrastructure or something to show them we mean business but will treat them decently if they surrender.
Hm. That didn't work. It's almost as if they think we'll mistreat them upon surrender. Well, what's next in the playbook... Here it is... Let's soften them up a bit with some indiscriminate shelling of residential areas to show them we're willing to murder civilians. Maybe they were hoping bad publicity would stop us, this'll convince them otherwise and they'll surrender in droves. We can still polish that turd.
What? Nothing? Ok, let's open the binder again... Hm, looks like we've moved up to carpet bombing and public executions with mass graves? Maaaan, that sounds like work. Whelp, better get started, this country's not going to murder itself. Gonna cost us, but when all's done, I'm sure there'll be oil and wheatfields left for the remaining Ukrainian slaves to work, just as long as we have something left for the oligarchs to split up.