If everybody followed your line of reasoning, not only Ukraine but half of Europe would be Russian already. Remember Putin's initial demand before the invasion was a full reset to the 90s. It was only because of Ukraine's dramatic fight that he scaled his demands temporarily.

Also, this logic doesn't work, because if it worked, he should already be satisfied by the annexation of Crimea in 2014. But he didn't, and this "success" made him even more hungry. It took time for everyone to understand this.