Even with a treaty in place, why would Ukraine not trying to become stronger with the Russian threat?

Because "getting stronger" in this context means militarily. Why would you want to bolster your military, when the Minsk treaty guarantees safety from russia? Not implementing the treaty and continued prospect of joining NATO, bolstering Ukraines military antagonized Russia, as they saw that the Minsk agreement got ignored. Merkel admitting that it was just to buy time, proved the Russians right.