Why would it be a bigger threat to Russia to have NATO on it’s doorstep, then it would be a threat to the Ukraine having Russia on it’s doorstep?
Ukraine is just a bit player on the frontier between Russia and the EU, and is merely the venue and proxy for the real contenders. Ever since the collapse of the Soviet Union, NATO has expanded eastward to encompass frontier countries that once formed a buffer between Russia and Germany. That is a very real threat Russia, which is not going to allow the West to advance closer to its southern borders along the Black Sea. If the shoe was on the other foot, we would have invaded two months ago.