The issue is that as someone already mentioned i doubt something like that was ever truly on the table.
I think you can’t give assurances like that in a vacuum. If a nation e.g. the US would grant them, they’d only do so while simultaniously building up a physical presence in the territory and possibly also do deeper integrations military wise. You wouldn’t give such strong assurances while weakening your own ability to act on them.
For Russia that would have never been acceptable.
Thanks for adding another source with some more context