It helps to reframe what 'winning' means for NATO. It does want to weaken Russia. But kicking Russia out of Ukraine as fast as possible wouldn't achieve that goal. In a war of attrition, imperialists can keep drip feeding weapons to Ukraine (bought with loans that will later be used to asset strip the country) and slowly bleeding Russia. (What NATO didn't account for is that Russia would win the war of attrition, but that's another issue.)
The longer the conflict, the more the US can prop up it's domestic military employment figures. It doesn't want to send soldiers to fight and die so much as it wants to create jobs in a way that lets the state funnel billions of taxpayer money (here, Ukrainian taxpayers' more than USians') into the military industrial complex. In other words, the longer the war, the more they line their own pockets.
Plus, thankfully, no other neighbour has been stupid enough to think it could defeat Russia in a conventional war on its own turf. Remember that Ukraine had one of the best militaries in the world before this fight, with recent, active military experience and a decade to stockpile arms and prepare for war with Russia. Imagine being tiny Latvia with 1.8m total population. Russia's active military is over 1m and rising. Latvia wouldn't stand a chance except as part of a whole NATO offensive. Even then, I would expect it to immediately consider withdrawing and becoming neutral to avoid being obliterated in that event.
As for Poland. Got to wonder whether Belarus would become engaged at that point. And if Poland gets involved, the war is going to get very close to Germany. And its politicians are cowards who are happy to send others to their deaths but have no interest in fighting themselves.