Because Russians are not Americans.
Definitely, Russians are not Americans. Russians where the ones who killed millions of Ukrainians by starvation, this genocide is known as Holodomor, google it if you want to know in detail.
And OP, I haven't been following the situation too closely as of late but I was kind of wondering the same thing as well. I would have thought that if the Russian resolve to conquer Ukraine was great enough, they would have employed blitzkreig tactics instead of whatever it is they're doing. They've got nuclear capability, FFS, so I don't think I'd be faulted for assuming that any country would rather surrender and not fight than risk something truly terrifying and devastating happening.
I'd be very interested to hear others' opinions on this, too.
I believe Pro-Russian people here will tell you: what adult goes full force when fighting mere children.
I think it's safe to say that the military capabilities of Russia aren't as great as it was advertised during the years. The government of Russia lies all the time.
Also, during the invasion of Georgia & Crimea, the West was only expressing their astonished feelings without actions. I think that Russia thought they would act as they did before, they would fulfill their goals and then everything would continue as if nothing happened. Now, the west supports Ukraine, giving them money and weapons. Idk if Russia really has full force somewhere hidden but if they have, it won't be wise to go full force because the world is watching, everyone is watching and it's definitely a red alarm for them, the world won't ignore full force bombing and war from Russia towards Ukrainians. Ukraine did nothing against Russia, they are just punished because they want a better future instead of Russia and their Soviet Union ambitions.