If this war is about Russia expanding its borders and capturing territory, why didn't Putin invade Ukraine in 2014? Why did he only take Crimea?

Every expert says that Russia could have easily defeated Ukraine in 2014. Certainly Angela Merkel, Francois Hollande and Petro Poroshenko thought so. They have all now admitted that the Minsk Accords were simply a ruse, a ploy to "buy time" in order to build up, arm, train the Ukrainian forces so they could take on Russia.

If Putin wanted to capture Ukraine, expand Russia's borders, and make himself a new Peter the Great, why did he sit on his hands for 8 years and watch the Ukrainians get supplied, trained and armed by the very best the US and NATO have to offer?