Putin even reaffirmed during a meeting on Monday with high-ranking government officials about this crisis that Ukraine is the West's proxy for waging war on Russia. Here are the five reasons why the US is still playing dumb:

1. Maintain Plausible Deniability For Escalation Control

Admitting complicity in Ukraine's invasion of Russia's universally recognized territory would make the US a direct participant in these unprecedented hostilities and thus place enormous pressure upon Moscow to respond against it and/or other NATO countries like Poland. The US doesn't want that to happen, ergo why it also forced Ukraine to call off its reportedly planned assassination of Putin last month as explained here, so dishonestly denying knowledge of its proxy's plans is par for the course and not unexpected.

2. Avoid Embarrassment & Responsibility Once Ukraine Fails

It's unlikely that Ukraine will be able to indefinitely hold the territory that it captured inside of Russia so it's a question of when and not if it fails. Accordingly, the US wants to avoid the embarrassment associated with that once it happens and also reduce the chances that Russia feels pressured to respond against it and/or other NATO countries as written above. The US is basically letting Ukraine hold the bag after everything inevitably fails apart so that Russia's full fury is directly solely against its proxy.  

3. Propagate David-vs.-Goliath Optics For Boosting Morale

By pretending to be caught off guard by what just happened, the US is lending false credence to the optics that the latest phase of the already decade-long Ukrainian Conflict that began almost two and a half years ago is a modern-day David vs. Goliath story. This is meant to boost morale inside of Ukraine amidst its drastic slump caused by the ramping up of forcible conscription there and increase support among the Western public for continuing to fund this proxy war in the face of growing fatigue.