The problem is that there's no realistic options in Ukraine.
If the only acceptable answer is 1991 borders, that's going to be an incredibly expensive proposition. The "economic isolation/sanctions will work any day now" strategy doesn't seem to be delivering, and any amount of defensive armament we could supply will be just chewed up for several years to come. Maybe if you give it another five years, Putin will finally lose interest or exhaust his resources, but in the interim tens of thousands more will die.
This war is expensive for Russia too, but for them it's a matter of national face-- this was a pretty blatant response to their sphere of influence being swallowed by NATO/EU expansion. So trying to get them to fold, especially when they have the stronger military position right now, is a hard sell. I'm not sure even resumption of trade/readmission to institutions is that big of a prize to offer, considering that their brand is pretty much sunk-- who's queuing up to buy Russian goods now?
We could lean into the idea this is about national face-- figure out the smallest concession Ukraine has to offer so Putin can declare a "victory" and de-escalate. But we're so adamant about 'we cannot reward the bully', or convinced that he'll keep trying for expansionism that we don't treat this option seriously.
There's a lot of belief that if Putin is allowed to keep a square millimetre of Ukraine, he will treat it as a license to keep pushing the border west. I'm not sure. We've proven that territorial conquest will be expensive and time-consuming, and I'm sure this has forced them to re-price all their assumptions. He has to finish what he started in Ukraine, but there's far less shame if he simply drops a hypothetical mission in Moldova or Georgia from unformalized future plans..