The reason that Russia is asking for an official position in writing is because there are so many different constituents in the US acting independently with their own agendas. Notionally Biden is in charge but even in this he has to deal with the Senate which is opposed to any deals with Russia. Then there are the intelligence services, the military contractors, the media, the moneyed interests etc. This is even more so with NATO which has even more dynamics.
Essentially what Russia is up against is a hive colony without a central Queen, and making a deal with one member is useless since they can easily be overruled/replaced by another.
This is why Russia wants things written down so that a couple of things happen:
1. There is some level of ownership of the issue from the Americans about what they say. A formal response from the US Executive is a place to start.
2. This will require some sort of internal discussions within the US to come to a common point of view.
3. Once written down, there is no confusion about what was meant or said.
In a way, Russia is helping the Americans/EU come to a consensus about their own posture, just like adults help children who are confused about what they want for Xmas. Write it down so we can look at it rather than yell it out different things at different times.
This is also why the US needs so much time to write things down – the state department draft has to be revised and grudgingly approved, if not signed off by all the various constituents.
