Here in this piece they say the Redskins made another offer in May, which topped the previous offer of $20M per season. Only the first two seasons were guaranteed, and the overall offer fell short of the $23.9M per season he's making on the tag.
So, just estimating, did the team offer him $22M per? I guess the guarantees weren't at the right spot, or it truly is about the money, or it isn't about the money and he wants out.
Kirk Cousins to play under tag after offer falls short - NFL.com
If the 'Skins got the feeling they were within $1M per year of getting it done, wouldn't they have just upped the offer? I think it was made clear to the team there's no number that would make him sign. I think this smells of Cousins being motivated to escape DC.