In Gaza and Ukraine right now, the colonial powers simply want the territory, and are largely indifferent or are openly hostile to the continued physical existence of the people who live there.
In Ukraine, since the point is controlling the land and not replacing the original population, non-violent resistance would not have stopped Russia but would have saved the Ukrainians most if not all the suffering and bloodshed.
Remember that the Russian aggression effectively started a decade ago after several successive country-wide popular uprisings in Ukraine which, despite violent crackdowns, strived for and put the country on the path towards democracy, westernization and reduction of oligarchic and Russian influence. Without wide popular support, the hundreds of thousands of soldiers and a large proportion of the population involved in the war effort would be just as, if not more, likely to turn on their own government. As a matter of fact, this is exactly what the Russians expected on the eve of their invasion, when the Ukrainian state was supposed to fold as a stack of cards and the Ukrainian people were supposed to accept their "liberators" without a hitch. Instead, Russia was instantly bogged down and pushed back by a determined popular resistance and a massive popular mobilization and the Ukrainian people are determined to keep fighting even after massive destruction of their infrastructure and hundreds of thousands of casualties.
Of course, the reasons for the foreign involvement in the war have much more ominous undertones and, especially in the case of the US, geopolitics are a major factor. However, one would have to be extremely misguided to pretend that motivations of the amorphous US political apparatus reflect the motivations of the Ukrainian (or even American) people in any way.